What a pain in the a**... Bluestacks should be banned for making it this difficult to remove. First, you need to hit Ctrl-Alt-Delete and stop the Bluestacks processes that are running. Only then can you go to explorer and delete their folders. Problem is, depending on where you installed the software, you will need elevated rights to delete the files. A good workaround is to go into the folders individually and delete them from within the folder. Then go back out and delete the folders. I had Bluestacks folders in C:\Program Files, C:\ProgramData and C:\Bluestacks. Delete them all.
Next, go to the root of your C:\ in Windows Explorer and type "Bluestacks" in the search field. Delete ALL of your findings.
You should now have no remnants of Bluestacks except that annoying entry in your "Add and remove programs". Why is it there? Because Bluestacks installer didn't remove any registry entries. So now hit Start->run->regedit
Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall and then you will have to look through each of the random alpha numeric entries for an indication of Bluestacks. It will be in the description on the right and there will only be one. You need to delete it. There is only one. DO NOT delete the wrong one. Finally, if you care to be tidy, remove all the Bluestacks registry entries under HKEY_LOCAL_MACHINE\SOFTWARE\Bluestacks.
Reboot and check add/remove programs to make sure it's all gone. Hope this helps.