I would personally recommend corn cob blasting. It is a non-toxic way of removing stain from your log home plus it wouldn't do any damage like pressure and sand blasting would. Water can damage logs and sand can leave makes on the wood. Corn cob is less abrasive and I think it is the best choice in removing stain. - L.R.
Buy a couple palm sanders, trust me you will need them. Oh yes you will also need a lot of sandpaper! lol
Before you go to stripping the surface down to the bare wood, you might try a little soap and water with a scrub brush and see how it looks after it dries. Some stains will come right off with little effort. Log Wash from Permachink is a great cleaner and won't harm your plants. You might need a pump sprayer and an extension "car wash" type brush to reach up high. Wash from bottom up and rinse from top down. A garden hose might be all you need to rinse the wall, saving the "fuzz" that a pressure washer might leave.
If you are staining over existing with darker stain, you might not need to strip to bare wood. Just a good clean surface for the new stain to "stick" to is needed. If you want a lighter stain than what you have, you might need to take down to bare wood. But in general, darker stains last longer and are more forgiving. Whatever stain you use, make sure it allows the wood to breathe. Once you get a color you like, put a low maintenance top coat over and rinse/clean your walls once per year and you might have to stain for another 7 to 10 years.
You might attend the next workshop the stain folks host for homeowners and applicators and learn firsthand the tricks of the trade.
I would recommend using a Lovitt's Cleaner & Brightner Kit to do a test to see if it will remove the existing coating, it is very strong and effective and costs very little, it would be a great place to start.
Look at my pics. I have Sikkens on my house 10 years ago. I Just posted some test pics of chemical stripper from Permachink. We used S100 eco friendly stuff. Thats what we plan on using on our whole house. We are using Lifeline Ultra 2 stain. Permachink offers free seminars we went to one it was great.