Don’t even think about removing the top. It would be a nightmare. Look for a plastic cap about halfway between the edge and center. Underneath will be a hex anode. You can inspect an anode without completely removing it. If you can see a couple of feet, it will give you a good idea of condition. Rule of thumb is to replace when you can see six inches of core wire anywhere on the anode.
I have a flexible anode that is good down to about a foot of clearance. That is what you would use at replacement time. Unless you like draining, disconnecting and tilting!