Iam using a 5wt 8’ rod with 5wt wff line and am getting 20-25ft cast most of the time.would going to a 6wt wfline help me or is that going to mess up what I’ve got now.I went out late this afternoon on a small local lake that the city han stocked for a kids fishing tourney about 3 weeks ago but it is so hot down here nothing was biting .no one was having any action ,not even the bait fishers 
the line should be ok. when it hot fish deep
When it’s this hot, fish deep, fish very early in the morning and/or very late in the evening. As a general rule, fish are a lot like you and me, they are most active when the temperature is most tolerable.