Pretty easy. remove rear wheel. Unbolt the swingarm. Pull out the bushings in the swingarm mountin points. Where it mounts to the frame and the linkage (the triangle thingy under the swingarm tha bolts to the shock)
The bushings are a long metal sleeve. Grab some grease and pack it in the hole wher ethe sleeve was(it is full of needle bearings) then carfully slide the sleeve back in teh greased hole full of nedle bearings and bolt it up.
the needls bearings may fall out if it is dry. No biggie, just put grease in there and line them back up. Grease holds them inplace until you put the bushing back in.
There is a strong possibility the bearings are shot though.
Grease once a year and avoid splaching in water and mud unless you plan on regreasing the bike before you ride it again.
Bearings with the sleeve removed looks like this (inside part, the outside is mounted in the swingarm and linkage).
Good luck!