The top button (#1 in the drawing) should unscrew from the rod (not 
shown) then the rod should drop out the bottom of the lift handle (#6). 
I don't think you'll need to do this if the problem is with the float 
button (#4). I believe the float button (#4) is just a press in deal, it 
should come out with a good pair of pliers.

If it's the top button stuck down you should be able to push it back up 
from the bottom. It's likely that the handle is rusty inside and or the 
spring (#2 in the drawing) is broken or weak. Look in the area around 
the ratchet (#8) for the bottom of the rod it should look like an "L" 
that catches in the notches in the ratchet. Push it up then you should 
be able to unscrew the top button.