Wow thatís cheap!
The existing wiring should be fine, just swap in another speaker. Careful when removing the female spade connectors, you donít want to force things and have them open up, thereby losing grip in future. There may be locking tabs on the spades to latch them in place / prevent them being pulled off accidentally; so they may need prying open with a small flat screwdriver.
Regarding your amp, maybe it has an unused 8 ohm output on the output transformer?