Float uses a service called Gravatar to set users' profile pictures. To update your profile picture in Float, you'll need to first update your profile picture in Gravatar.
Step 1: Authenticate your email with Gravatar
Go to Gravatar, and click Sign In. If you already have a Gravatar account (or a WordPress account), log in. If you don't have one, you'll need to create a new account. Make sure to use the email that you use in Float. Gravatar will send you an activation email - the sender will be WordPress. Follow the instructions to activate your account.
Step 2: Set your profile picture in Gravatar
When logged into Gravatar, navigate to your profile page where you'll be able to set a profile picture.
Step 3: Clear your browser cache
If you're using Chrome, click on Chrome > Clear Browsing Data > select Cached Images and Files > Clear Data.
Step 4: Log back into Float
You'll now be able to see your profile picture!