Please explain in more detail what you want to change.

When I installed the program I used a particular email address, now as I have several different email addresses, I wish to use a different one to use the program, and not the email address that the program was setup to use. So the question is can I change the email address that Thunderbird checks or do I have to re-install the program to make this change?

Add the new accounts starting from File/New Existing Mail Account. Once you have one or more accounts set up, go to Tools/Account Settings, select one of the new accounts in the left pane, then click Account Actions at the bottom of the pane, Set as Default. Then, select the account you first used, Account Actions, Remove Account.