Some suggestions - instructions for all these are available on this board.
1) Change the oil. It has probably never been changed. Mine (78K miles, 12 years old) shifts much more cleanly after an oil change, especially when cold. Get decent oil - Motul Gear 300 75-90.
2) Bleed the clutch, get some new fluid in the cylinder. It may be disengaging very late. The clutch should disengage in the middle of the pedal travel. If you need "foot to the floor" then there is air in the system.
3) If the pedal is "heavy", follow the instructions for pulling out the top bush and dribbling oil down the clutch shaft.
4) There is a known problem with swarf blocking 4th gear selection that has caused many gearboxes to be needlessly replaced. It is a bit more involved than the above fixes, but still only an hours works. Not sure if this starts as a synchro problem.