To get DeSmuME to stop lagging, go to Configuration, then Frameskip. Set the frameskip to 9, and limit the frame rate. That should get DeSmuME to a speed where it almost never lags, and never goes too fast.
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you can't mabye download it again
You can't. Desmume 9.7 doesn't have a cheat code option. You should probably download an earlier version of desmume if you want cheat codes on your game.
Get a job and buy a better internet router.
Try servers that aren't as busy. Or try a different computer if possible.
get a faster internet and/or get anew PC