To install the Forum do the following:

1. Download the latest Kunena Component
2. Go to Extensions > Manage > Install and install it
3. Extract sandal_extensions.zip from the package you downloaded from Themeforest. You'll find a folder named 'kunena' and within it a package named canvas_kunena_template.zip
4. Go to Components > Kunena Forum > Templates and click on 'New Template' button
5. Click on choose file and select canvas_kunena_template.zip then click on 'Upload File & Install button
6. Once the install is completed, select the Canvas template and set it as Default template