If the shocks are of the same stock length, then replaceing them one side at a time is the easiest way. Doing it one side at a time helps to hold the suspension height in check and help in removing and installing the shock. If they are lowered shocks you will have to remove both shocks completely. First you need to support or place a jack under the rear of the engine, high enough to take the weight off the rear wheel. It is best to have a buddy or two around then because when you go take off the shocks, you will need someone to support the weight of the swingarm as it will be free to drop to the ground with the shocks removed. The same person will be needed to help raise the swingarm to help align the shocks to their mounts. *Do not remove both shocks without supporting the weight of the bike from underneath or from the top with some type of hoist* A little Antisieze on the bolt threads wouldn't hurt either. Bigern PS> Lifting the bike can be tricky, take your time to find it's best balance point. You need only to lift the rear enough to take the weight off the suspension. Leaving the kickstand down and letting the bike lean over on it helps stabilize the bike.
I have another trick for jacking up the back. I put the lift under the engine where the tabs stick down, but this mainly lifts the front off the ground. When you get the front off the ground about 3 or 4 inches, attach a ratchet strap to the rear end (preferably the luggage rack) and then to a rafter and lift the rear end of the bike off the ground. This works well for me and the bike seems to be stable. Dave 06 Classic R&W
If you have the standard springs they should be fine at where you have them. I have the same length shocks and weigh the same. I didn't have any problems even with them cranked all the way out to the softest setting. It is more about how the ride feels to you for me it was nice to actually feel the swing arm move and work as it should. However I did run into problems when I had a passenger. I set them at the highest setting and they would still bottom out over curbs (with a passenger that weighed 125 pounds). I eventually got the HD springs because of this.
It may of just been me but that 1/2 inch difference was really noticable the first time I got on the bike and made the bike feel low. I like it.
I had neither jack, nor available friends, nor rafters. Actually, one of my friends has an I- beam and a come-along in his garage and I almost did that. However, I brought it to a bike shop and the guy did it zip-zip-zip for $35. He used Loctite on the threads. At $350 for the Progressive 412's from MAW, that worked out well.