It wont hurt it to have the fluid level checked & replaced completely first but as with all things like this, drive it around to get it warm first & then park up some where you are happy to leave it (i.e. your drive) should it take a dislike to the process.
Make sure the main box is in Nuetral before changing to 4WD.
Should be OK but probably very stiff, I know mine was. The more you do it the easier it should get.
Just go through all the positions & drive it a little in 4WD hi, then try 4WD low BUT only either on loose ground so it can slip when the wheels are turned or in a straight line on tarmac or you will damage it.