Repetition Day

Hey, Joe, so glad you decided to do this forum.
My question is on repitition day, i chose wide grip bench and i started with a weight that i could do 28 reps with. After how long should I change up the exericse?
once i get to 35 reps for the first set?

Also for supplemental exercises on all days how often should you change the exercises?


I would like to know this also.