Finally a question that I get. The carb's upper chamber all unscrews, the little brass screw stays. You can release the clamps and turn the carb towards you a little, or pull the whole carb out. The whole top cap of the carb comes off and the slide will still be connected to the cable. The top cap should come off with your hand twisting it. Smash the spring that you will find between the slide and the cap, all the way compressed. hold the spring compressed to the lid of the carb. push the slide toward the cap for some cable slack and with a little jockeying the cable will come free of its notch.
If you look into the top of the slide, you will see a 6mm nut. That holds the needle in the slide. remove the nut and you will find the needle with a circlip stuck in one of 5 grooves. That clip is very hard to find if it shoots off there, so be careful. I lay it flat on a countertop and push the needle down while covering the clip with my hand, flip it over and snap the needle into the clip.
Moving the clip up one position will lean the mixture in mid range by lowering the needle into the hole, thereby restricting fuel flow a little bit.
When you put it back together, insert the needle and fasten with the 6mm nut, you have to again, smash the spring to the lid, then get the cable into its notch, then align the little plastic deal that keeps the cable from coming out of that notch. Make sure the throttle spring goes all the way down. Drop the slide back in there and screw the cap back on.
If this is the first time, you have been in the carb, it would be a good idea to pull it out all of the way and look it over for dirt and debris, or wear. Also good to note what jets are in it, and clip position, for future reference. I always snap the throttle a few times to make 100% sure that its working properly before starting it back up after messing with it, too.