Is it just hard to pull the gear lever out of gear and put it into gear,
but the transition in between is OK, or is it stiff all the way through the
throw?
If it is the former check your fluid level in the master cylinder
reservoir. The same reservoir feeds the clutch and brake master cylinders.
If the fluid is too low you'll get very bad clutch action because you're
getting air in the lines as well as fluid. You may have to end up replacing
the clutch master or slave cylinder or both, because fluid will be leaking
out somewhere.
As far as I know there is no adjustment for hydraulically operated
clutches. But you can try pumping the clutch pedal a couple of times before
trying to pull the lever out of gear (might work as a temporary fix), then
double de-clutching on the downshifts.
Cheers,
Steve C