18 Photoshop Biohazard Brushes 200 to 700 pixels How to install brushes (.abr files) : 1. Put the .abr file you’ve downloaded into the folder /Users/{username}/Library/Application Support/Adobe/Adobe Photoshop CS3/Presets/Brushes (on mac OS X) or C:\Program Files\Adobe\Photoshop\Presets\Brushes (on Windows) . 2. Then open your Adobe Photoshop, active brush tool, go to option palette and click on to open the brush preset picker.