To bump up your long runs, try adding 1 or 2 miles per long run for two consecutive long runs, then come down every third long run to your earlier distance. So if your long run is currently 12 miles and you want to increase it, you could go to 13 for the next one, then 14 the one after that, but then back down to 12 for the next one. This will better allow you to adapt to the longer long runs than plowing ahead with longer and longer ones week after week.