How do i change shifts at walmart?

so i have been working at walmart for a little over a week now and i work overnights stocking in the grocery aisle. well its really not working with my schedule. i know i took the job but thats because i needed it and now it just doesnt work with my schedule and im going to be starting some summer classes soon and working overnight wont work for me. so how would i go about asking to change from overnight to first shift? do you think they will work with me cause if they dont switch me then i probably will quit. also how long will it take them to switch me?