The rear diff, transmission and 3pt hydraulics are a common reservoir. There will be a drain plug on the bottom of the transmission and probably also one on each final drive housing to the rear wheels. There will also be a screen filter for the hydraulic system low on one side of the trans, it'll prob be a banjo style fitting going thru a line into the trans housing. Pull it and clean it in solvent or diesel. Use Kubota UDT or equivalent if you have auxiliary hydraulics or just 80w90 gear oil is fine if not. The front diff will have a fill and a drain plug, use 80w90 gear oil. Each front wheel case will have drain and fill plugs, use 80w90 gear oil.
I'm unsure of capacities but you can probably find them in an online service manual if you don't have a hard copy.