Cisco IP phones

Dear Experts,

I have old cisco IP phones (7945 and 7911), it was configured with old
call manager, now I want to connect it with a new one but could not
change the call manager IP from IP phone configurations. I also tried
it to do with tftp but don't know where to bring the template to
upload on tftp server.
Secondly is there anyway to reset these phones completely.
Thirdly can i configure extension so that if someone login with his
credentials get his extension from any IP phone.

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Thanks & Regards,
Asim Zafar
Blogs and organic groups at http://www.ccie.net