How do i put 16 or 17 inch rims on my silverado?

i have a 92 with a 350 tbi runs beautiful and i just put 1k into the motor but it sits low it has factory 15's its a 2 wheel drive and really has no capacity i know how to redo the springs but am not sure about how much is involved in stepping up the tire size buddy siad i may have to go from 5 lug to 8 wondering whether this is necessary or not?