I have a Cabela's Traditional II 9' 5wt rod, a White River 7'6" 5wt rod, a Cabela's RLS2 5wt reel and a White River 5wt reel and I am wondering if i can use a 4 weight line or maybe even a 3 weight line in these. Would there be any types of problems using a lighter line then the rod and reel are rated for?

This is because i dont have enough money to purchase any new rods or reels at the moment and I have realized that a 5wt line is a little heavy for the size of the fish that I catch around here.