If you want to reduce the length of your watch, you can do it yourself without the help of a watch repair shop. All you need to do is to first identify which links you want to remove. Then, find the screws holding those links in place. You can then remove the screw using a 1mm screwdriver so you can completely remove the links. Then, reassemble the watch strap properly.
If you don’t trust that you can do the strap alteration properly, getting the service of a watch repair shop is not that much of a trouble. It could only cost around £8 to £12 and won’t take too long.