Assuming you have used the Epic Games Launcher for your initial installation of the Unreal Engine 4.21, updating to Hotfixes follows a similar method.
- Open the Epic Games Launcher
- You may immediately notice the yellow button that normally says “Launch” now says “Update”. If so, just click it.
- Otherwise, click on the “Unreal Engine” option on the left sidebar, and then click on the “Library” option on the top bar.
- You should see your 4.21 engine slot here. If it is not already listed as 4.21.2, then it should give you the option to update.