What is the $WINDOWS.~BT folder?
This seems to be Windows update logs & files.
It includes files to upgrade Windows, and also, once you do upgrade, the old OS goes into that folder
It should be perfectly safe to delete it, as long as you don't want to upgrade or downgrade Windows.
However, you can't do it the normal way.
Instead,
a) Press Windows key + R
b) Type: %windir%\system32\cleanmgr.exe
c) Hit Enter on your keyboard
Edit: This method seems to only delete some things in this folder, some may be left over. See the other answer for a more complete removal method, though that isn't perfect, either. Additionally, this may help: How to delete trustedinstaller files on Windows 8
Sources:
- http://answers.microsoft.com/en-us/windows/forum/windows_8-windows_install/how-do-i-delete-windowsbt-after-failed-windows-8/d15416e8-fd5a-4d4e-b04b-5907a4f6c623
- John (see comments)
- FranKee (see comments)
Well, I got as much as 4.4 GB in it. Looks like Windows 7 is “pre-loading” Windows 10, though I never agreed and explicitly disabled it...
CleanMgr.exe
mentioned in the other answer deleted some stuff, but mostly refused. Manual install in File Manager also failed, because of lack of rights (even with full admin privileges), lack of ownership (owned by “TrustedInstaller”), etc...
Here is a brief receipe, to help yourself from windows command prompt with administrator rights:
// go inside that folder:
cd /d "C:\$Windows.~BT"
// take over ownership
takeown /f *.* /R /D Y
// (go for coffee, takes a minute)
// grant full rights to everyone
icacls *.* /grant Everyone:(OI)(CI)F /T
// (coffee?)
// and all other subfolders, just be careful with use of *, naturally.
rmdir Sources /s /q
// actually, I got a few errors with rmdir. Things went smoother
// with this Unix-like ´rm´ executable in your path,
// coming from unxutils.sf.net
rm -r -f *
// after all has been wiped, also remove the parent dir
C:\$Windows.~BT>cd ..
C:\>rmdir "$Windows.~BT"
// checking...
C:\>dir /A:DHS
Volume in drive C is Windows
Volume Serial Number is ####-####
Directory of C:\
15/07/2015 19:15 <DIR> $Recycle.Bin
30/07/2015 16:39 <DIR> Boot
04/08/2015 08:35 <DIR> Config.Msi
14/07/2009 07:08 <JUNCTION> Documents and Settings [C:\Users]
01/11/2012 09:35 <JUNCTION> Dokumente und Einstellungen [C:\Users]
01/11/2012 09:35 <JUNCTION> Programme [C:\Program Files]
04/08/2015 08:35 <DIR> System Volume Information
0 File(s) 0 bytes
7 Dir(s) ########### bytes free