Find a LH bottom bracket cup. I used a knackered HT2 cup but a traditional cup and cone one, or the loose LH cup from a square-taper cartridge are fine too. Screw your freewheel onto the LH cup and then you can hold it with the appropriate BB tool while you unscrew the cone with a pin spanner. The cone has a LH thread so the freewheel won't come loose on the BB cup as you unscrew the cone.
When done remove the freewheel from the cup using its own removal tool (generally 4-lug BMX or Shimano UG splined).
To retighten the cone when all cleaned and regreased, hold the sprocket with a chain whip while screwing the cone i nto the body.
Caveat: don't use an Italian or Raleigh BB cup. You need a normal ISO/BSC threaded cup, which is the same as a freewheel hub thread.
