Hello and welcome to the Forums
If you are talking about a screen lock password, then after a fixed number of incorrect entries your device should prompt you for the password for the gmail account the phone is registered to. If that doesn't work, shut off the device, log into the gmail account on a website and change the password using Google's Password Recovery
Once the new password is confirmed, turn on the device and try using the new password. The above does rely on you having either 3G or WIFI enabled on your device, and if it's not, the only other solution would be a full factory reset!
I hope this helps!