Are you replacing the woofer? I'm assuming, yes? Those wires have connector-clips on the ends and they can be very, very tight. I grab them and firmly but gently wiggle-pull them off the tabs. Before you do that tho, make sure you mark or make note of which wires went on each tab! Very important. Also, I'm sure you know, but turn off and unplug your sub first.
That's my way. You do want to be careful not to break the plastic or those tabs. Sometimes they're tough to get off. I've even seen them covered in a dab of clear silicone. If you want to wait a bit someone else might know of a trick or tool.
