how to i switch from formula 1 to formula 2 for my 2 week old baby?

my 2 week old is on cow & gate stage 1. its been good and all. but last couple of days his feeds have gone from every 3hours to every 2hours. i tried giving him a little more coz he only takes 3oz, but he spits it back up. so im thinking its time to move onto stage 2 for hungry babies. says its suitable from birth..... so i bought the tub and im ready... but i dont know what to do??? do i just switch or do i need to sort of wean him over? like 1 scoup of stage2 and 2 scoups of stage1. i know you will all say ask your health visitor but i dont see her until friday.