- remove the battery (exposing the mount)
- support the gearbox with a trolley jack
- remove the three bolts/nut.. the nut in the centre of the mount will likely be tight - 'shock' it round to start it. the nuts that hold the mount to the alloy armature aren't captive, so you'll need to catch them as they fall from underneath
- remove the old mount (may need to huft things about to get it off)
- once it's off, tighten the exposed shaft - there's a flat on it. it screws into another nut under the gearbox (difficult to get to)
- replace mount
that's about it for the upper gearbox mount. is that the one?