Change password to Time Machine backup

Could someone provide me with step-by-step instructions to change the password to my Time Machine backup/retrieval?

From a previous post, it has been pointed out that this could be one of four different password - Encryption, Disk, Base Station or Wireless.

I am not referring to the Encryption password. I am not referring to the Wireless password, as my understanding is that that is the password to the Airport router.

I need the password that refers to the one that needs to be entered when the Mac arrives back from repair with the hard drive wiped clean. (That is once you realize that the factory left the OS at 2 revisions back from what you backed up on, so once you realize that, you need to upgrade the Mac before attempting to restore.)

My current password is too long, so it became annoying when going through the above mentioned troubleshooting.

Disk? or Base Station?

Thanks.