Are you using POP or IMAP for your email?

I am using iamp for my e mail and it still deletes them from server

Imap email is server based. You remotely view messages with email clients like Thunderbird. If you delete a message from a remote device or the server the result is the same. The message is removed from the server. When using IMAP there is no option in Thunderbird to Leave Messages on the Server. They only exist on the server. That option does play a part and is available only when using POP.

can i change my e mail to a pop3 account and solve this problem??

What exactly are you trying to accomplish?

I have multiple devices that I am downloading mail to and want my wife to be able to download them onto another computer. What may be of interest to her is of no interest to me so I would delete them on thunderbird. Is the cure as simple as me not deleting them in thunderbird and then she will be able to view them??

Yes. As stated above with imap you are viewing message on the server. Delete them from any device and they are gone. Maybe you need to Google imap and learn how it works.