Would help if you told us how they're fitted... On most modern bikes, you undo the topcap, and then tap the top of the headtube to let the forks drop out. - As the headset will have a wedge piece to hold it all together, so when you'd tighten the headset, it'd all get wedged...etc. If it's got one of those horrible stems, where you tighten to top bolt, which widens the piece inside it.. then you need to take the stem off, then undo the headset on the threaded steerur. Once you've undone those two bolts (usually with a 30-32mm spanner?) then the forks should just drop out?