Upgrade your old Two10 (4 or 12 ohms) to a switchable Two10S version with this switch kit!
This is not a quick swap but it's not that difficult. You have to remove the grill and both 10CR speakers. You have to remove the spade connectors and capacitor/inductor from the speakers. You then have to remove the backplate (the rear dish the speakons are mounted in) and pull it out along with the wiring loom.
Then the new wiring loom needs threading through from the back and the spade connectors attaching to the speaker terminals (as marked). Then screw the backplate on. Bolt the 10CR speakers in. Re-fit the grill. And don't break anything, cross-thread bolts, push out t-nuts, strip screw threads, drop any tools on the woofer cones, etc. So go slow and carefully.
Never do this when you're in a hurry before a gig or band practice, it is guaranteed to go wrong and a mistake could be v expensive!