check its level with the gearbox warm and just after you've moved the selector through all the positions leaving it for a few seconds in each one and then back to park.
if it needs draining off there's a plug under the gearbox
Also if you're not sure when the fluid was last changed I'd get something fresh in there as often the fluid spec may have changed- Speak to the local dealer and parts dept - they will advise you on the updated fluid to use..
Hello Paulif the oil level is too high then it'll get whipped up and aerated so the oil pressure at the transmisson oil pump will drop as its pumping air not oilthis results in a poor shift quality and actuators not workingso yes try draining the old fluid off and replacing with fresh and the normal procedure is to fill using the side fill plug on the side of the transmission
dropping off the sump pan and cleaning out the filter screens is a good idea as they do clog up over time and this too can result in poor quality shiftsor if you have a fluid transfer pump with a long thin probe then you can empty and fill through the dipstick tube