First loosen the Top Triple Clamp bolts that hold the fork in the Triple clamps. Loosen the cap at the top of the fork tube. Don't take it off, just loosen it.
Then once the wheel, brakes etc have all been removed, take the fork out. Loosen the cap at the top of the forks completely and drop the outer tube down as far as it goes. You will need to seperate the cap at the top of the forks and the nut just underneath the cap, by putting a spanner on the bottom nut(17mm spanner) and a spanner on the fork cap. Turn the cap anti clockwise and the nut underneath clockwise, and once loose, screw the cap off completely.
The spring will then come out, and the tube in the centre of the spring will slide down. Push the tube all the way down as far as it goes, and then using a thin ruler or something straight and non flexible to measure from the top of the outside tube(compressed all the way down) into the tube, and see what the measurement is between the top of the tube and the oil level. It should be 100mm. If there is less oil than that, add 5wt fork oil in small qauntities, and pump the centre rod up and down a few times slowly before re-measuring the oil height until you get the oil to 100mm from the top of the outer tube. Pull the centre rod/tube back up to the top, and quickly drop the fork spring back over it and into place. It may drop down a bit by itself, so just use a size 14 spanner and fit it between the coils of the spring and onto the shaft of the centre rod, and turn the spring until the rod is at the top. Then put the cap back on and tighten it onto the centre rod, by turning the cap clockwise while holding the nut at the top of the shaft. Then screw the cap into the top of the fork and put the fork back into the triple clamps and tighten everything. Assemble the front wheel/brakes, but dont tightn up the locking bolts on the front axle just yet. Tighten the size 21 nut at the end of the shaft, and then pull the front brakes and bounce the front forks up and down quite a few times with the front brakeon to align the forks and wheel properly. Then tighten the locking nuts on the axle and make sure the nut at the end of the axle is also tight.
This is just to check the oil height etc, seal replacement is a bit more involved, and for that I would suggest a manual. If and when replacing seals, be sure to check that the shafts of the forks do not have any chips on them which could be damaging the seals.