I've done it on an L5740, so hopefully the same?
Inside the cab, all around the perimeter, are a bunch of bolts. 10mm if I recall correctly. Most, but not all get removed. The hardtop has captive nuts molded into it, and the bolts are machine screws, so once loose, will unscrew by hand. If any of the bolts continue to pose resistance, then they are probably NOT the bolts you need to remove. Once they are all removed, the top just lifts off, but a helper will make it easier, including a check to be sure you got all the bolts out.
Note that the top os a molded shell - like two halves of a clam shell, and you really can't get into it. The only access is through the vent filter at the very rear, and it offers very little access. I'm not sure how you plan to afix your light bar, but if you were planning to thru-bolt it to the top, it probably won't work since you can't access the hollow interior.