It is very to remove your Windows 7 operating system (OS) and leave Windows 10 your lone OS in your PC. If you have a dual boot computer, every time you start it, you will need to select which OS to start, or you can just leave it, and Windows will automatically load the default OS after some seconds. But if you wanted to remove this dual both and stick to only one, then the steps are all below.

For this tutorial, you can also do instead of removing Windows 7, you can remove Windows 10, or whatsoever OS you have there in dual.

Remove Windows 7 from Windows 10 Dual Boot

1. First, Backup all your important files, just in case something went wrong during this deletion process of the operating system.
2. After you back up all the files, click Start
3. Type MSConfig in search or Cortana and press ENTER
4. Click the Boot tab.
5. Click Windows 10 and click "Set as default" button to make it your primary OS (operating system). After clicking the Set as default button, you will now see that your Windows 10 has the Current OS; Default OS label.
6. Now, click Windows 7, and press the Delete button. Then click Apply and then the OK button.
7. If the Restart and the Exit without restart buttons appear, just click the Exit without restart for now.
8. Go to Start, click File Explorer. It is the icon above Settings.
9. Under "This PC," find your Windows 7 drive.
10. Right-click your Windows 7 drive and click Format.
11. In the Format configuration, leave all the fields and do not do anything else. Now, press the Start button.
12. There will be a warning saying: "Formatting will erase all data on this disk. To format the disk, click OK. To quit, click CANCEL." Press the OK button.
13. When the Format is completed, just press the OK button.

Your Windows 7 drive is now empty, we will put the empty allocation left by your Windows 7 to your Windows 10 drive, by extending it. Follow the process below.

Note: This is OPTIONAL. If you think this is quite complicated, you can skip this tutorial and just try the last option below.

1. Right-click "This PC" and press Manage.
2. Inside Computer Management, find Disk Management and click it.
3. Find your Windows 7 drive there. When you find it, right-click the drive and click Delete Volume. Just click YES to confirm the process. After deletion, you will now see that it has the "Unallocated" label on it.
4. Now, right-click your Windows 10 drive, and press Extend. If Extend is not clickable or grayed, then you need to download and install EASEUS Partition Master 14.5. The password for the zipped file is lace12.
5. After installation, open the Easeus Partition Manager.
6. Inside it, locate Windows 10 drive, and right-click on it. Click Resize/Move.

7. On the image below, you will find the black dot with a vertical dotted line. You just drag that dot to the left.

8. After dragging the dot all the way to the left side of the unallocated space, you will see the image below.

9. Click the OK button to continue.

10. Click Execute 1 Operation.

11. Then, click the Apply button.

12. In Operation Progress, just wait for it to finish.

13. In the Warning, just click the Yes button.

14. Your PC will restart with the screen below. Just wait for the process to finish. It will take some time, so you can leave your computer for a while.

15. When done, your PC will start automatically. You can now check your Windows 10 drive, and it has all the unallocated space left by your Windows 7 drive that you removed earlier.

If you do not want to EXTEND your Windows 10 drive, you can just format the deleted Windows 7 drive and make it just a normal drive, where you can install future programs, and save your files. Follow the steps below.

1. Again, right-click "This PC" and press Manage.
2. Inside Computer Management, find Disk Management and click it.
3. Find your Windows 7 drive there. When you find it, right-click the drive and click Delete Volume. Just click YES to confirm the process. After deletion, you will now see that it has the "Unallocated" label on it.
4. Again, right-click the Unallocated drive, and press New Simple Volume.
5. Click Next.
6. Next again.
7. Another Next, and then Finish.
8. You just created a fresh and new volume. You can check it by going to This PC and see all the displayed drives there. The one with no used GB is definitely your newly created drive.

EASEUS Partition Master Mirror links: