Challenge I have a windows.old folder on my computer and I am running out of HD space. Should I remove it and will removing it cause any problems?
I was looking for anything that might be common to the systems that refuse to upgrade. I know of one computer (not mine unfortunately) that has not allowed an update to take hold since Windows 10 went into the free upgrade mode. It updated to Windows 10, but now refuses to take another update. That computer is on an M.2 SSD with Norton 360, but that's all I know. I have not been able to check that system out yet.
Windows 10 Anniversary will tell the user that you can continue to work as the update is applied. I think you are better off shutting down all programs and even rebooting before applying the update. When it goes wrong it might be just a little problem, or it can go straight to the BSOD mode.
Norton seems to be a common issue. I keep trying to get people to go with ESET, but they cling to Norton. In the case of the original W10 install that has never updated it was Norton 360 and I suspect that is at least part of the problem.
Concerning Windows.old you should think about this before proceeding. If you think you might need to restore to the old version then you want to keep that folder. You might also want to do some research on moving files or folders that are in that path. Rather than move them I would reinstall, but I know that is not always an option.
The proper way to remove the folder and clear up that huge amount of space it is using would be to use the Disk Cleanup routine and to search through the available options for "Previous Windows installations."
What I did was to use the update (W10A) for about a week, or until this last Friday, and then I did the Windows Reset. Bear in mind though that I keep all of my libraries on various drives so nothing would be lost. The immediate effect of a reset is that only windows remains and it is in a pristine state. So, instead of having twenty-one Adobe products and seventeen Autodesk products slowing down the boot process by adding services and background processes, the boot is straight forward and much, much faster.
Windows 10 A. has the advantage of including the Bash shell, which has several geeks I know of all giddy inside and out. I like the new Dark Theme, which allows me to leave the system running at night without causing the entire house to glow. The systems that I have changed MBs in require a call from MS-India (I believe) because even the new Activation trouble shooter cannot cure that problem, but at least there is a troubleshooter now. Edge does have new plugins including Netflix, LastPass, and Ad-block, which really had problems before the update (at least for some people). If you have a tobii eyeX or similar facial/eye recognition device your system will now log you into properly prepared websites without a password (biometric authentication). Personally, I prefer the TPM modules to biometric. The most important to me is the Windows Ink, but a lot of the promised functionality has not materialized yet. Cortana has been improved, but I shut that off within the first 20 seconds of W10A, but not completely (BECAUSE YOU CAN'T!!!). And Now Cortana has taken over my phone too. Universal Skype has swallowed my remaining Skype credits in favor of my Xbox/Live account, and I have not discovered how to recover that yet (time issue). The Start menu has gotten rid of the "All Apps" method in favor of immediate access (and more advertising), but I do like what they have done with Money, Weather, Alarm, and so on. I have not looked into what Continuum can do for me yet, but it seems promising. Xbox Play Anywhere brings Xbox games to your PC (this is really big at the moment). The Notifications and Action Center are better integrated even with non-Windows mail apps, which also makes the Calendar more useful (properly setup it can also broadcast to any PC on your network should you be at a different desk during an alarm event). Probably there is more than that which just aren't coming to me at the moment.