You cannot change your UnVale username, your profile's URL. However, you can change the display name on your profile's main page. To do this, you use the "Edit..." dropdown menu, and choose "Edit profile." After you click this, you can see all of the editable fields on your profile. There should be a little pencil next to your display name, and you just type what you want there instead!
If you are wanting to use a different URL you would have to make an account with your new username, and speak with staff to archive the account that you no longer wish to use. This is essentially the same as deleting the account, and would free up the username to be claimable again.
UnVale's team of developers is hard at work, constantly introducing and improving new features. Thank you for joining this journey with us, as we strive to make Space for All!