change network card?

[isellmore59]

I tried changing ip address and it changes,but after a while it changes back to old ip address.I have a speedstream modem and linksys router.
If the network card in computer is what isp uses to assign ip address,
couldnt i change network card in computer and that should change ip address?
I have not tried the all night thing.Ebay suppened me when ip went back to old one.