You will need some solvent to break down the grease. Gasoline, mineral spirits, parts washer, stay away from water based degreaser due to there acid content, it can damage bearings if they are not compatible. Fill best you can, turn the wheel back and forth ( drag link unhooked for easy turning ) to stir the mixture. You may end up pulling the bottom cover or side cover if there is no drain plug so be aware you may need to make a new gasket. If the grease is clean inside, add a little gear oil, it will mix into a slurry, a 50/50 mix will be about right.
