Hi and welcome,
If you have the very same license version of LE and AI, you even don’t have to install Cubase AI. Cubase LE, AI and Elements is one application (executable). Only the license decides, which functions are available.
Yes, you can open your Cubase LE project in Cubase AI and use Cubase AI instead of Cubase LE. There are only few advantages, but there are some.