When you purchase Grafton from ThemeForest, you need to download the Grafton files from your ThemeForest account. Navigate to your downloads tab on ThemeForest and find Grafton.
Click Downloads to see these two options. Installable WordPress file only. You can upload this file when you install the theme. All files and documentation (full zip folder). You will need to extract and locate the installable WordPress file to upload when you install the theme.