You can change the userID (adobeID) and password under user account / My Information.
Log in to FormsCentral with your current AdobeID/password, select the person icon on your upper right corner, the "My Information" dialog will show. Here you can have another person enter his/her information. This other person will need to create/confirm his/her Adobe account first.
Hope this helps,
Thank you! That helps alot!