Boot up CS2 and head on over to the settings in the main menu. You’ll want to select the Keyboard / Mouse option from the menu and then Movement Keys. Here you can change what your jump is bound to.

The Jump command is assigned to [SPACE] in CS2 by default, but if you want to re-bind jump to your mouse scroll wheel, you can do so using either the in-game menu or the console. However, using the ...