Windows...BT and windows.old

To delete windows.old right click on start, click run, type "cleanmgr" no quotes click ok. The disk cleanup will come up, select the drive you have W10 installed on, click ok. When the disk cleanup box comes up click on "Clean up system files" the process will repeat itself except this time you can clean up the big files, windows previous installations and another one that escapes me at the moment.

Those can take up a lot of disk space, as much as, or more than 12G. Since I've been using W10 after each update to the next build I delete those files. The partition I created for W10 is 30G and with an installation and the windows old files it can take 20G+ so I delete it to make room for the next build.

C:\$Windows.~BT is where Windows 10 is installed from when you upgraded to a new build. Not required but the install.esd in the sources folder can be used to create a ISO that can be used to install the same version on other computers using the ESDtoISO tool.

Windows.old is where your previous Windows installation was saved when you upgraded. If you don't need anything from there you can delete it using Disk Cleanup.

CmmTch, Ztruker
Thanks to both of you. I have hurriedly put the thread without search After search, I fould the same solution as you have suggested. I could clean up and save nearly 6 Gb space.

Once installed .ESD changes to all the files necessary to install windows (same version) again. Instead of converting ESD to ISO i just made ISO with all the files from C:\$Windows.~BT folder and moved to another HDD.