OK, so, you’ve tried a Linux distro for netbooks (like Ubuntu) and you’ve decided, “Hey, I don’t like this.” I’ve been there, too.
But now, whenever you boot, you get an annoying GRUB menu asking you to select what OS you want to boot into, and you have to scramble to switch to Windows 7. Plus, you’ve got a swath of disk space you can’t use anymore because the Linux distro you don’t want any more is using it. Most people would advise using a Windows repair disk, which isn’t really helpful on a netbook. (But if your netbook runs Windows XP, you’re going to have to make a Windows XP USB boot disk or boot from your vendor’s recovery partition either from the BIOS menu or from an entry in GRUB; the manufacturer’s manual will tell you how to do that).
The good news is if you run Windows Vista (unlikely, as it wasn’t shipped with many netbooks) or Windows 7 (much more likely), you can uninstall Linux from your netbook without a repair CD. To do so, boot your netbook and select the Windows 7/Vista entry. As soon as you do this, start hitting the F8 key until you reach a startup options menu. From that menu, choose “Startup Repair” (normally the first option). Windows setup will then load, ask you to select your language, and, if you have a password-protected account, ask you to log in with that account. From there, select “Command Prompt” and in the prompt run the following:
The system should respond with “The operation completed successfully.” Close the command prompt and choose the “Restart” button to continue. At this point, your netbook should boot directly into Windows 7 without GRUB appearing at all. Once Windows has started, right click Computer in the Start menu and choose “Manage.” You’ll need to “Allow” this if UAC is enabled. From the left side of the window that appears, choose “Disk Management” under “Storage.”
At this point, you should see all of your drives listed, as well as the one or two primary partitions, without any label or file system information. You can now delete these to recover the hard-drive space from your Linux installation. DON’T delete any entry marked "recovery partition," however; these are restore tools provide by your vendor to allow you to reinstall Windows if necessary — you want them around. Once you’ve deleted the Linux partitions, you’ll see a healthy chunk of free space on your drive. You can select the NTFS partition nearest this block from the free space, right click it, and choose “Extend volume” to add this free space to your volume.
That’s it! Linux is now totally removed from your netbook.
Addition 1: Windows won’t let me use “Extend volume” after deleting Linux
This can occur in a number of situations, including having the free space to the left of the partition to extend or if Windows has decided to store system files at the end of the partition. If this happens, you have two choices.
Your first choice is to make a new drive in the empty space and assign it a new drive letter. This will make the additional space appear as a second drive in "Computer," and you can use it that way (although it won’t give you additional space in your primary partition).
If your heart is set on expanding your primary partition, your best bet is to use GParted, humorously enough, from whatever USB drive you used to installed Linux in the first place. Use the “Try” or “LiveCD” option of the distro, open a terminal, and run "sudo gparted."
Select your main drive from the top-right drop-down menu. This will let you expand the main partition as you see fit. (Don’t delete any partitions from here). Once you’re done, you can save the changes to the drive and restart. Chkdsk will probably run the first time Windows starts; this is normal and doesn’t mean anything is wrong with your drive.
See also: Using GParted to Resize Your Windows 7 or Vista Partition (How-to Geek)