Instructions
Open the "Starcraft 2" editor by navigating to the "C:\Program Files (x86\Starcraft II" directory or the directory where you installed "Starcraft 2" on your computer, and double-clicking the "Starcraft II Editor.exe" file.
Open a map by clicking the "Open" button on the toolbar, selecting the map you want to increase the unit damage for on the Local Files, Battle.net or Campaign tabs and clicking "OK."
Press the "F7" key or click the "Data" icon on the toolbar to open the data editor window.
Click the "Data Type" box, and select "Units" in the list.
Select a unit by clicking its name in the pane at the top left corner of the data editor window.
Scroll down in the bottom left pane, and locate the "Effects" section.
Click an effect that includes the word "Damage" in the Effects section. Units with multiple attacks or abilities have multiple damage effects.
Increase the number in the Amount field on the Combat pane at the top right corner of the data editor window.
Repeat this process for each unit ability you want to increase the damage of.
Click the "Save" button on the toolbar, and save the map to your computer.