I want to update my iPhone 5s to iOS 13

Your iPhone 5s can only update as far as iOS 12.5.7

Here are two different ways to ensure the highest iOS that your device will support is on your device.

Update your iPhone, iPad, or iPod touch wirelessly. Click here --> Update your iPhone or iPad - Apple Support

Here are instructions about how to update your iPhone, iPad, or iPod touch with the Finder on a Mac computer --> Update your iPhone, iPad, or iPod touch with the Finder - Apple Support

I want to update my iPhone 5s to iOS 13

This is not possible. The iPhone 5s can update as far as iOS 12.5.7, but that is all that it can do.

If you need to run higher iOS versions, you will need a new phone.