Q: i chaneged the password on my phone and i forgot it and  locked my phone

If you cannot remember the passcode for the Screen Lock, you will need to Restore the device...

1)  Connect to iTunes on the computer you usually Sync with and Restore...

http://support.apple.com/kb/HT1414

2)  If necessary Place the Device into Recovery mode...

http://support.apple.com/kb/HT1808

Note on Recovery Mode.

You may need to try this More than Once...  Be sure to Follow ALL the Steps...

Once you have Recovered your Device...

Re-Sync your Content or Restore from the most recent Backup...

Restore from Backup  >  http://support.apple.com/kb/ht1766