How do i switch phones with a CDMA phone?

This cannot be done unless you change the hardware itself. CDMA and GSM are two different technologies used by the carriers and it's a difference in the hardware that makes it not possible for you to convert a CDMA phone on GSM, or vice versa.

i just bought a htc evo 4g and its a cdma phone.I am taking it along with me to Europe and i know it may not be used there,but a friend of mine told me it could be converted to gsm only if a space behind the phone can be created and also other features would be formated before i start using it.so i think cdma could be converted to gsm