If you've previously installed a build on Kodi, we would recommend doing a clean install in order to prevent any problems occurring and for you to fully capitalise on the best possible performance from this particular Kodi build. As aforementioned, The Beast is one of the most comprehensive builds out there and it's one for the whole family to enjoy.
First of all, you'll want to register yourself on The Beast website, where you'll then be able to install The Beast build for Kodi through my steps outlined below. Note: you will need to verify the email address in order to move forward – spoof email addresses such as firstname.lastname@example.org won't work!
1. Open Kodi and navigate to System | File Manager | Add Source.
2. Select "None" and enter or paste http://thebeast1.com/repo/ (make sure it's entered as is, or else it won't work), then click Done.
3. You should also see a box underneath, where you'll be able to "Enter a name for this media source". To make life easier for yourself, rename it "Beast" and then select OK.
4. Go back to your Kodi homescreen and go to System | Add-ons | Install From Zip File. From here a list of folders should appear – be on the lookout for the one you've just added.
5. Click on the folder (if you haven't renamed it, it might appear differently), and then select the file called "plugin.video.beast.zip".
6. After you've completed the task, you should see a notification saying "Wizard enabled".
7. Return to the homescreen and go to Programs | The Beast Wizard. You'll want to highlight it and press C (secondary click, or long-press), to then be presented with the "Add-On Settings".
8. Now you'll need to add the email and password you used when registering on its website.
9. Once you've added your details, click on "The Beast Wizard" and the build should start to download, extracting and installing itself too (on Android devices, you might be prompted to unplug and plug the device – press OK to continue). You might be also asked to back up your current build – I would always suggest backing up!
10. You might experience a few reboots, where your Kodi device will have to restart. Once complete, The Beast will be fully installed and operational on your system.