how can i update old version final cut pro x to latest verision 10.15

Make sure you are signed into the App Store with the Apple ID used to purchase the application. Click the user icon in the lower left of the App Store window. This will take you to your purchased page. Find the application there and download it from there, not from the FCP page.

FCP can be updated in the App Store. Just open the App Store in your mac, login with the Apple id, click on Updates and then click the Update button next to FCP.

Your other question is rather strange. A library is a file on your drive. You don't need to delete it to update FCP.

You can delete it if you are sure that nothing in there is of any interest to you. Just drag the file to the trash.

Of course, if you do that you will lose any projects and video files that were in there. Is that what you want?

You have to download it from the App Store if your computer supports it.

You bought the computer from Apple with the application preinstalled?

If that’s the case you should contact support from the App Store to make sure your Apple ID is associated with the application purchase.

The computer most likely does not need to be fixed. Using support you will need to find a way speak to or use chat to contact Apple support. As the computer was purchased from Apple in Kuwaití it may be linked to the Kuwait App Store not to the Nepal store. I’m sorry I just don’t know and I believe only Apple support can help you.

Did you previously buy FCP? If you did, you can update it and don't have to pay again.

If you have been using the application and need to continue using it to finish work in progress, there is a free trial version that’s good for 90 days. https://www.apple.com/final-cut-pro/trial/

Start here

https://getsupport.apple.com

You don’t have to remove the library. It will update to the newer version.

The application can’t be transfer from one user to another. It may have been left in the computer, but it shouldn’t have been, and you don’t own it.