The best way to take it off is to leave the forks on the back, slacken the allen bolt on the top triple T clamp, then get a wrench on the cap (preferably the box end, or a socket), and undo it only a few turns.
Then slacken the bolt on the lower triple T, take the fork out (I'm assuming wheel and mudguard etc is all out of the way), then with the fork out, hold the stanchion in one hand, and apply downward pressure on a socket on the top cap while unscrewing it the rest of the way.
There will be some pressure on the top cap when it comes off, because of the fork spring.
Just a word of warning with these fork caps that they are very soft aluminium and are quite easily scuffed at the corners of the hex heads.
If you use a twelve point (double hex) socket on them they will almost certainly be damaged. If this matters then you are advised to use an ordinary open ended spanner (wrench to our American friends) or else a six point socket if available.
I have used both methods and the caps are still pristine after using the spanner.
Also be aware that the caps can be easily cross threaded when re-engaging them with the fork tubes, a little care pays dividends.
Unless you are planning to remove the fork springs or are disassembling the fork for seal replacement, you don't need to loosen the fork cap before removing the forks. Simply loosen the pinch bolts on the upper and lower triple clamps and slide the forks down. This is assuming the wheel and fender have already been removed. If you are installing fork boots, you would simply slide them on then reinstall the forks.
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