I used to keg in Sankes for a while, still do on occasion but they are a bit harder than corny kegs. To remove the spear you're going to need to do a couple things:
1. Vent the gas out of the keg, this can be done by turning it upside down and using a large wrench (1" or 24mm works for me) to depress the ball.
2. Using a flat head screwdriver try and remove snap ring in the neck of the keg. Be careful because sometimes they're in there really tight and you don't want to break off your screwdriver head in the opening. Start on the side closest to the exposed end of the ring.
3. Once the ring is out, twist the spear (about an 1/8-1/4 turn) so that the retaining nubs line up with the opening in the neck.
From there you can clean it like a corny keg.
My suggestion is to use it for a fermentation vessel. If you disassemble the spear you'll find that the tube separates from the part with the nubs on it (let's call it the cage). You can reinstall the cage and an air lock bunge will fit perfectly in there. I do this all the time and it's hands down the best fermentation vessel I've used (no infection-plastic, unbreakable-glass, won't melt-better bottle).
Hope this helps!