In this video I show you the two different ways that the Air Arms S200 can be adjusted for power. The gun used in this video is a Mk1 and the anti tamper on these was not used. On the later model Mk3 there will be anti tamper that will need to be removed before any adjustments can be made. This is a simple job to do if you have access to a dremel and flat head screw driver. You can buy aftermarket hammer adjustmers from a few different places online, including Ebay below.

Below is a link for you to buy a 4 way utility key that can be modified to remove the rear stock if you don't have the correct tool that came with the rifles when new. The tools can also be purchased online, but cost around £14, so the utility key adaption is just a cheaper option. Tesco sell these in their cheap tools and parts section of the store, or you can buy one from here:
https://www.ebay.co.uk/p/3026223188

Hammer spring adjuster replacement:
https://www.ebay.co.uk/itm/AirArmsS...

Genuine Air Arms S200 Stock removal tool:
https://www.ebay.co.uk/itm/AirArmsS...