Perch Password on local host

I have installed perch on my Mac, everything installed fine and was able to test the site and log into the CMS on my machine. On my return the next day my login for the CMS wouldn't work (details incorrect) I have looked in myphpadmin and the username is correct (I know the password is correct i made a copy of the details)

Is there any way I can reset this from the database, without having to reinstall?

Any one had any similar problems?

Thanks

Jon