The carb probably has limiter caps. If you don't know what you're doing, it might be best to have a saw mechanic take a look.
If your determined to try to fix her yourself, first check the saw over for problems. Completely blow it out, remove covers and blow some more, check impulse line and intake boot for air leaks, check fuel filter and tank vent, check fuel line, remove and disassemble carb looking at internal filter screen, operation of diaphram, fuel pump. Remove jets and gently blow out and inspect for problems. You may also want to check for air leaks at the main seals. Go to madsens.com and learn how to fine tune the saw.
Good luck.