Power up the switch
press esc before flash boot. it will ask for 3-5 seconds before boot.
enter the password recovery mode [press 3]
then go back and restart your switch
The switch wont ask you password on next login.
then you can configure your new password with:
(config)#username user1 password your_password privilege 15
if you want to erase all config of the switch:
press Y for delete startup config
(switch will reboot)
then it will prompt whether you want initial config with wizard or not.
you should config via wizard or manually.