The Park tool FR 1.3 is compatible with SunRace freewheels and others. The through hole of the tool is large enough to work around most axels used in a freewheel system so removal (or putting it back in) isn't required.
Typically it takes a great deal of force to break loose the threads of a freewheel, which tightens itself as you pedal the bike. This is why it's suggested to place the tool in a bench vise, place the wheel onto it and use the wheel to apply torque. Another option to turn the engaged freewheel removal tool is a 1 inch box wrench (that's just a typical wrench with one end open, the other a circle with the interior splined or with flats that mate with the wrench flats of the tool). Perhaps a more commonplace option would be using a crescent wrench (adjustable wrench). If the freewheel has been on awhile, it would be fruitless to attempt a wrench removal if the wrench is less than a foot long. The freewheel threads are standard, right-handed threading so counter- clockwise rotation will loosen/unthread the freewheel.
If you can't remove the freewheel, the bearing race (cup) on that side is still accessible for cleaning and greasing and bearing replacement by removing the axle assembly and using needle-nose pliers or something similar to reach the cup. You'll need (9) 1/4 inch bearing balls per side.