Either you can read the instructions or watch this video:
All Downloads below
You must have a clean version of Bluestacks
There is a chance you may need to uninstall and reinstall Bluestacks to try again!
1. Install Bluestacks and make it run
2. Once it shows the GUI and is running leave it open
3. start program BSMultiTool.exe
4. once open press 1
5. then wait for it to ask if you are ready to root and press any button to continue.
6. Wait for the rooting process to finish and DO NOT TOUCH BLUESTACKS WHILE IN ROOTING PROCESS!
7. After rooting is done press Q on rooting software
8. open Root Checker App.apk with Bluestacks and check if it is Rooted
9. Once verified that is has been successfully root congrates
Here is where you can find the latest version of BSMultitool: