If you had registered your Cubase LE 4 on your MySteinberg account, you should be eligible to install the latest version of Cubase LE, however you will have to request from Steinberg that the license be converted from the old Soft-eLicenser to the new Steinberg Licensing system.
Cubase LE is no longer “versioned”, in other words, a license for Cubase LE will always allow the “LE” edition of the latest release to be used. See also the following post: