The top must come off first, that's correct.
I like to insert two thin flat objects (while still in the Beocord so you will only have to use three hands),
and then lever it off. Alternatively, use a small electronics sized cutter and bite just below the plastic top.
The plastic tops are quite flexible and will take a lot of abuse without breaking.
Remember to get the little brake pawls on the correct side of the reel table flanges
when you put it back in the Beocord.
Martin