You first need to enter your current password in order to change it, but If you have a backup of your brainkey you might be able to restore/recreate your wallet with a new password, I think that the brainkey can't help you if you imported your account from 0.9.3.c
One last think is to double check the passwords you type, especially if you had them written in paper, a lot of typos can occur 9g 5s, c(, l1 etc