My Windows folder takes up too much space - how can I reduce it?

A large Windows folder is quite normal. The Windows folder may start out in the 6-8GB range bbut it will grow larger over time. This is normal behavior of Vista/7 and there isn't really much you can do about it.

The cause is winsxs, and the details are described in this blog-post.

For comparison my Windows folder is 29GB, a bit bigger than yours.

The recommendation of running Disk Cleanup in the other answer are worth a try, but I suspect winsxs is the main cause of your large Windows folder.

EDIT Filling in from the comments:

Another folder that can grow big is the Windows\Installer folder, a protected system folder that contains repair and uninstall information for the programs and updates you've installed. There used to be a program by Microsoft called miszap.exe that could clean out orphaned files from here, but there were issues and it is no longer supported.

The fact is that there really is no safe way to clean out stuff from the Windows folder beyond what Disk Cleanup can do. It is also quite normal for the Windows folder to grow over time as updates and programs get installed onto the system.

The one way to get the Windows folder back to a smaller size is to wipe the system and clean-install it from scratch. But even this is a temporary fix as the Windows folder will start to grow again over time.

To keep it from growing too much it is worth installing windows from media with the latest service pack installed and to be frugal in what programs are installed.

A couple more suggestions.

1. One of typically large subfolders of Windows is Installer (a hidden system folder). You can move it to a larger drive and replace it with a symbolic link. Here's a cmd command to create the link once you have moved the folder:
   mklink /D C:\Windows\Installer D:\...\Installer
   It's an archive which isn't used often, so moving it to a slower drive won't hurt your performance.
2. Check the LocalMLS folder (C:\Windows\ServiceProfiles\NetworkService\AppData\Local\Microsoft\Media Player\Art Cache\LocalMLS; the "Art Cache" part is named differently in non-English Windows). It can also grow large by keeping thousands of images. You can delete them all (it's just a cache, no important data), and if you don't use Windows Media Player Network Sharing, you can disable their collection in the future. Run services.msc, find "Windows Media Player Network Sharing Service" in the list (in Russian it's "Служба общих сетевых ресурсов ..."), stop it, then open its properties and change the Startup type item from "Manual" to "Disabled".

If you run low on disk space do the following:

Turn off hibernation on desktop PCs:

powercfg -h off

Remove old service pack files:

DISM /online /Cleanup-Image /SpSuperseded

Commands must be run from an elevated command prompt.

Run "disk cleanup"

Run ccleaner.exe from http://www.piriform.com/CCLEANER

I just reclaimed about 20GB of space on my machine.