If you mean the desktop password, from the Desktop guide:
If for some reason or another you forget your password, the following steps can help you recover.
To recover from a forgotten password:
1.Turn on your computer. If it is already on, press Ctrl+Alt+Del.
2.Watch the upper-left corner of the screen. When you see a small white box, press Alt+F1.
3.When you see the Recover Choices screen, press F2.
4.Type CD\OS2; then press Enter.
5.Type MAKEINI OS2.INI LOCK.RC; then press Enter.
6.When you see the Successful completion message, restart your computer by pressing Ctrl+Alt+Del at the same time. Your lockup password is removed. Now you can set another password.
Note: Because it is easy to remove a lockup password, it should not be your only means of protecting the information on your computer. Use the Lockup feature in combination with other security features provided with your computer, such as a power-on password or a keylock.
If you mean the File and Print Client, in eCS you can use the Local System-> Install Remove-> Post Installation tasks to create a new administrator ID and password. I haven't actually tried that, but you may need to fist remove the Access control file. Go to a command line, and do NET HELP BACKACC, NET HELP FIXACC, and NET HELP RESTACC. I think something there should give you an idea. Chances are that doing that will initialize your network to all defaults, so you will need to set it up again.