Rear spring replacement help

[thorns]

Just replacing the rear spring with a heavier one for my weight.
how do I get the spring retainer off the bottom of the shock?
Have seen a few vids where the retainer has a slot so you can imply slide it off, but this is a solid piece.
Do I need to unscrew the bottom of the shock off the shaft?

http://i650.photobucket.com/albums/uu229/thorns82/IMAG0050_zpsd8493b4a.jpg (http://s650.photobucket.com/user/thorns82/media/IMAG0050_zpsd8493b4a.jpg.html)

[pete376403]

Is that a hex nut immediately below the collar? Hold the bottom mount ina vise then undo the nut (it looks like a lock nut) then you should be able to unscrew the bottom mount, unscrew the nut and slide the retainer off.

maybe.

[thorns]

That was my initial thought as well, but then there is the clicker etc in the nottom piece, so not 100% unscrewing it is the way to go?
Most other shocks it seems really simple, the retainer has a slot in it and you can just pull it off sideways.

[thorns]

Another quick question on rear shocks. How do you know if you need to re gas it as well?