your 5 MM T need to be about 16 " long to reach the bolt head. To replace the forks you need a 5 or 6 MM Allen key to loosen the bolt in the stem ,back off 5 turns, hit it with a hammer ,the stem will drop down, pull up to remove, put aside for the time being. Now you need 2 32 MM wench or a 12 " crescent wench to remove the locking nut. remove any spacers, remove the adjustable nut, watch out for bearings than may fall out as you remove the forks. clean out the cups and bearing of grease. Use a hammer and a punch to remove the race on the forks if the replacement forks don't have one . Repack the cups and bearings with fresh grease and reverse what i have told you. Good luck.