You can only upgrade to the latest version, but it allows you to run all past versions of Cubase Elements. When you upgrade to Cubase Elements 9.5, your Cubase LE 7 will automatically become Cubase Elements 7 without having to install anything.
But I would strongly recommend giving Cubase Elements 9.5 a try. Installing it wont replace Cubase Elements 7, so you can continue using your old program if needed.
Cubase 9.5 greatly improves the CPU and graphics performance compared to Cubase 7, and it also fixes many of Cubase 7’s design and workflow issues based on user feedback. You can configure it to function just like Cubase 7 (for example, opening editors in a new window instead of the lower zone).