Update My MacBook Pro

The ability to update depends primarily on your computer's sub-model, which your have not shared with us. Older Mac cannot run the latest operating sytem.

So that we can give you an effective answer specific to your devices, please tell us the sub-model and the current macOS version, quickly available form "About thisMac..." under your Apple menu:

For security reasons, please DO NOT post a serial number here.

To upgrade beyond macOS 10.13 High Sierra, your Mac must be a 2012 or newer sub-model.

What happens when you try updating?

Try suggestions given in this article. https://support.apple.com/en-us/HT201541