700s are a no go- its a 26" mtb with canti studs on the frame and fork.
The bottom bracket is either 68 or 73 wide. My 2 Ascent frames(90 and 91) are both 73 wide, but dont know for sure for yours since if I am thinking of the frame, yours is older and may be 68 wide. You can simply measure or pull the spindle and check what is stamped on it.

As for changing the crank to something different- a warning- The Ascent had different sized chainstays thru the years from year to year and as a result, you need to get a crank that will fit in the chainstays. Not all cranks will.
What gearing do you have and what do you want to change it to?

For the freewheel(guessing its a freewheel), as mentioned, that limitation is based on your rear derauilleur and how much chain it can eat up when using the smaller cogs.