You have two connections to take loose, one at the sender end, and one at the hard line on the body end. Both are a real pain in the butt to get loose. The fitting material is soft, and the force required to break them loose is very high. The only way I've found is to use flare nut wrenches, two of them, on the line hut and one on the sender plate line/body hard line. Flare nut wrenches look like box ends with a one flat gap in the box. This grips 5 of the 6 flats on the connector and gives you a chance (not a good one) to break it loose. IIRC, one is a 19mm, and the other is a 15???.

I'd make sure I could find a new hose before I took off the old one. If you can't find one, I'd try to fix your old one. THis involves cutting off the crimps with a dremel cut off wheel (without nicking the hard nipples), peeling off the old rubber hose, and putting on new fuel injection hose with double hose clamps.