Yes welcome to the forum chief77,
It needs changed yearly.
Are you asking of which fork oil to use or how to do it?
You'll need to include a bit more info as to your riding style, sporty or soft mushy ride, payload, Progressive springs or stock springs?
Here is a link to a thread on how to change the fork oil through the air caps at the top of the forks. Just jack the front wheel off the ground and remove the drain plug at bottom of fork. To refill just remove the air cap and valve core and put fluid back in through there. Quick and easy... no need to remove the forks or fork cap to do the job.
Note: For the 95 and up models the fluid level is wrong. It was corrected in a later thread. Here is the corrected amounts for the late model 1500s. 14.0" for 95-up (progressive springs installed tight end down)
14.2" for 95-up (progressive springs installed loose end down)
14.3" for 95-up (OEM springs installed)