Use a multimeter, set the meter to read in the high ohms range, somewhere above 10k and 1m ohms. Touch the meter leads to the corresponding leads on the capacitor, red to positive and black to negative. The meter should start at zero and then moving slowly toward infinity.
Usually it easier to just buy a higher amp controller. The YK43B is my favorite and it looks like they are available again on eBay:
https://www.ebay.com/itm/Electric-E-Sco ... 0005.m1851
(Here's the item description showing that it handles 24 - 60 volt)
http://vi.vipr.ebaydesc.com/ws/eBayISAP ... cureDesc=0
A big heads up though, the YK43B will dump a HUGE
amount of amps to your motor! You will
pop a wheelie if your not careful!
However, if your like me and you like to do things just "because", you can replace the fets to increase power, but it's a lot of work and you need a good soldering iron. The shunt can be modded to increase power. summerbear48 did a nice write up here: