I purchased a home with a Craftsman remote garage door opener that is outside the garage. Model # 139.53876 with push bottons 1-0 (no # and no *). I know the old four code number but need to know how to change the code with a new code number.

Here you go:
http://www.managemyhome.com/mmh/lis_pdf/OWNM/L0707407.pdf

Press the 4 buttons for the present password, then press and hold the # button
The open light will blink twice
Press the new 4 digit password you have chosen, then press enter
The opener light will blink once when the password has been learned
Test by pressing the new password, then press enter.