I agree with M.B.Doc, unless the shocks are leaking, leave them alone. Try changing the accumulators.
Unlike regular spring shocks, self-levelling hydraulic oil shocks do not need to be changed in pairs. If one is leaking, only the offending schock needs to be changed.
About a DIY job, be careful, the system is set at an incredible high pressure and it does require a good tech to know how to bleed it.
Do a search on the subject to gather more info.