Well, it's kinda up to you, they are fairly easy to swap out. If they aren't leaking they are probably OK.
One thing you don't want to do is allow the axle to 'hang' on the seal, when you slide the axles out, slide them far enough to clear the seal before allowing it to hang (or pull them all the way out).
Going back in just be very careful and slow. The splines can sometimes nick the seal, OR you can inadvertently knock the spring off the back side of the seal.
Just take your time and you should be GTG.
