Instructions
Open "World of Warcraft" by opening the "WoW launcher" and clicking "Play" in the bottom right corner. Wait for "World of Warcraft" to initialize, which can take a few minutes.
Log into your "World of Warcraft" account by typing the credentials of your Battle.net account into the fields.
Select your character from the character log-in screen and click "Enter World."
Press the Escape key on your keyboard and select "Key Bindings" from the list of options.
Scroll down to "Camera Functions" about halfway down the list and click "Mouse Wheel Up" next to "Zoom In," then click "Unbind key"; do the same for "Mouse Wheel Down" next to "Zoom Out."
Click "Okay" then "Return to Game." Log out and log back in to make sure the changes are permanent.