You can change account name on the page https://www.donationalerts.com/dashboard/general
It is possible to use specified service once per 60 days.

Please, pay attention that the new nickname you select should meet the following requirements: it should comprise from 3 to 20 symbols and can consist only of Latin characters (A-Z), numbers (0-9) and underscores ('_'). The first symbol can comprise only Latin characters (A-Z) and numbers (0-9).