Hey there, let's walk through this step by step to get you back to Windows 7 without losing your data—don't worry, we'll take it slow and safe!

1. 先做最关键的一步：全量备份你的数据 #

Even if we're aiming for a "non-destructive" process, accidents can happen (like a power outage mid-partition resize). So first, grab an external USB drive or another storage device with enough space:

• Use Ubuntu's default file manager to manually drag-and-drop all your important files: documents, photos, videos, downloads, and anything in your /home/your-username folder.
• If you prefer using the terminal for a more robust backup, run this command (replace your-username with your actual Ubuntu username, and /media/external-drive/backup with the path to your external storage):

  rsync -av /home/your-username/ /media/external-drive/backup/
  

Double-check that all your files are on the external drive before moving on!

2. 缩小现有Ubuntu分区，腾出Windows 7安装空间 #

Ubuntu's built-in Disk Utility makes this straightforward:

• Open the "Disks" app (you can search for it in the Ubuntu menu).
• Locate your single hard drive partition (it'll be the one with the Ubuntu logo and most of the disk space used).
• Click the gear icon and select "Resize Partition".
• Drag the right-hand slider to the left to free up space—Windows 7 needs at least 20GB, but I'd recommend 30GB+ for updates and apps.
• Click "Resize" and wait for the process to finish (don't turn off your computer during this!).

3. 从Windows 7启动盘引导并安装 #

Now it's time to install Windows 7:

• Plug in your bootable Windows 7 USB stick, then restart your computer.
• When it boots up, press the key to enter the boot menu (usually F12, Del, or Esc—check your computer's splash screen for the right key).
• Select your USB stick from the boot menu to launch the Windows 7 installer.
• When you get to the "Where do you want to install Windows?" screen, find the Unallocated Space we just created.
• Select that unallocated space, click "New" to create a partition, format it, then proceed with installing Windows 7 to this new partition.
• Important: Do NOT touch the existing Ubuntu partition here—if you delete or format it, you'll lose all your data!

4. 恢复数据并整理分区（可选） #

Once Windows 7 is installed:

• You should be able to see your old Ubuntu partition in Windows Explorer (it might show up as a "RAW" drive if you don't have EXT4 support—you can install a free tool like Ext2Fsd to read/write to it).
• Copy your backed-up data back to your new Windows 7 partition, or directly access files from the Ubuntu partition if you installed the EXT4 tool.
• If you don't want to keep Ubuntu anymore, you can open Windows' Disk Management (right-click Start > Disk Management), delete the old Ubuntu partition, then extend your Windows 7 partition to fill the entire drive. Only do this if you've confirmed all your data is safely moved!

备注：内容来源于stack exchange，提问作者Charlotte