just wanting positive insight

wanting some of you fellow threaders opinion on something... well i have two account with verizon one with one line with udp and i transfered my upgrade from that account to the one with 3 lines {no udp} and upgraded to an s6 and currently waiting for it to be delivered.... so what is the actual steps to take to keep the udp and not loose it. do i just swap out sim card out before turning the phone on after recieving it??? or what?? like i said just want some of all your personal experiance and insight on the take?