Your username is what comes after the '@' symbol in your profile link, e.g. wakelet.com/@phil. 

To change your username:

• Go to wakelet.com/home and click View Public Profile on the left. 
• On the page that opens, click Edit Profile. 
• Type in a new name after the @ symbol. 
• Click Save. 

And that's it! The Edit Profile options also let you change your profile picture, header picture, displayed name, bio and social links.