Fitbit is updating two of its most popular fitness trackers.

The new waterproof Flex 2 and heart rate-tracking Charge 2 are available now up for preorder and will officially go on sale in the coming weeks.

With the Charge 2, Fitbit redesigned its Charge HR with a larger display that makes the tracker look and feel more like a fitness-focused smartwatch. It has the same heart rate monitoring capabilities and smartwatch-style notifications (for incoming calls and texts) as its predecessor, but the bigger display combined with the overall slimmer band make the tracker feel a lot less clunky.

The tracker is also much more customizable than previous versions -- you can easily swap out the bands (it comes in black, teal, blue and purple variations) and customize the watch face. Fitbit will also sell additional leather bands (in brown, indigo and pink) for $69.95.

The Charge's fitness-tracking abilities have also been upgraded with new features that are able to record specific types of workouts, like weightlifting, runs, bike rides and interval sessions, and the tracker will automatically recognize some types of activities like yoga and running.

Additionally, the Charge 2 is designed to evaluate your overall fitness level by estimating your VO2 max, a metric typically used by professional athletes that measures how much oxygen you can use during cardio activity. An accurate VO2 max measurement typically requires specialized equipment in a lab setting, but Fitbit uses its heart rate and other profile information (like your age and body weight) to provide an estimate the company says is pretty close to what you would get in a lab environment.

If the Charge 2 is more fitness tracker than you need, Fitbit is also releasing a new version of its smallest tracker, the $99.95 Flex 2. The Flex 2, a redesign of 2013's Flex wristband, also has the distinction of being Fitbit's first swim-ready wearable. The company says the tracker was designed to be water-resistant at depths up to 164-feet so it should be able to handle most water-based activities.

The most immediately noticeable change with the Flex 2, though, is its size. The already-slim tracker has been pared down significantly -- the tracker itself is now 30 percent smaller and its accompanying wristbands (it comes in small and large sizes) are similarly slimmer.

Like the Flex before it, the Flex 2 eschews a traditional display in favor of a series of LED lights that indicate your progress throughout the day. But Fitbit has managed to upgrade the minimalist display with some new powers as well. The tracker will provide notifications of incoming calls and texts via different types of vibration and light patterns.

The notifications will be far more subtle than what you get with Fitbit's other trackers, and we haven't had enough time to truly test the feature out yet, but it's a clever addition to Fitbit's smallest tracker.

The Flex 2 is also more customizable than the previous version. Like the fashion-centric Alta before it, Fitbit is giving its customers more options to make the tracker look more like jewelry than a wearable.

In addition to the standard range of different colored bands -- the Flex 2 comes in black, navy, lavender and magenta color variations -- the company is selling optional bangle and pendant accessories that disguise the tracker as jewelry. The bangles come in silver ($89.95), gold ($99.95) and, of course, rose gold ($99.95). The pendants come in silver ($79.95) and gold ($99.95) options.

For a cheaper accessory, Fitbit is also offering three-packs of its "classic" wristbands for $29.95 (a single color band will run $14.95.)

Speaking of accessories, Fitbit is announcing partnerships with a few new designers for third-party accessories for its Alta. Public School, will make watch accessories and Vera Wang is designing a collection of accessories for Kohl's. Both will go on sale later this year. Fitbit will also reboot its partnership with Tory Burch, who will have a new line of accessories launching in early 2017.

Finally, Fitbit's app is also getting a significant overhaul. The app will now give Apple Watch-like reminders to move each hour and the app is adding a new "Adventures" feature to its app. The addition is meant to offer a challenge-type feature for users who don't want to compete in the existing in-app competitions. Instead, adventures will push users to complete in-app goals based around step count and other activities.

With stiff competition from the smartwatch space, Fitbit is doubling down on its fitness trackers with more smartwatch-like features and fashionable styles without encroaching entirely into smartwatch territory.