The best way is to remove each cylinder and work it up and into a pail to purge all the oil out.
Another method, if your loader is hooked up power beyond, is to remove the drain or "T" line from the loader valve, attach a hose again into a pail, then run your loader and cycle it to purge the old oil out. be sure to run your cylinders full stroke each way and you will soon have them full of clean oil.
( remember to keep topping up the reservoir as you do this)
Ed