use an ftp program and what dash are you using? anyway with the ftp program fetch the config file in E:/dashboard/ and then use notepad and edit the old password to some thing like 1234 then upload the file and it should work fyi this is for unleashx and xbmc but i havnt tried it on any others but it should work
or (thats a way to do it) the easy way is go to E:\Dashboard\Config.xml in youre file explorer on the xbox
open the file and fing the sub menu with the password you forgot and 1. copy it down and use that 2. edit the file there and reboot
using this you can even take of the password