Most people hang on to the old version for a month or so, until they feel good with the new version, and then deep six it. There are three major elements in LR's operation: the downloaded and installed software "the version". the Raw files that you supplied, and the catalog of information that LR wrote about those files (with your guidance for the most part.) Adobe keeps all its old versions forever available on "Legacy" or "Heritage" sites. If you remove LR 5 and later want to reinstall it, no problem, if you still have the registration key. The Raws remain by you no matter what. But if you convert your LR5 catalog to a LR6 compatible catalog, LR6 first copies the old catalog and then converts the copy. An LR6 catalog won't work in LR5, so keep the LR5 catalog even if you uninstall LR5.