Your only option for LR/PS now in 2019 is the subscription model that includes both (LR Classic and Photoshop) at $9.99 / month. There are more expensive plans, but for the software you only need the $9.99 plan. The new software does not overwrite or update your LR5 software. Rather, it installs into a new and separate directory. When you open the new LR software, it will detect the existing LR5 catalog and will ask if you want to import that existing data into the new software's catalog. You can choose no. Even if you allow the import, the highly recommended action, nothing about your old LR5 software and catalog are updated / modified.

You can encounter quite a bit of confusion trying to keep both software versions active. The new LR software doesn't remove your old LR5 launch icons. So, unless you take corrective actions, you could easily end up working in one version when you meant to be in the other.

If you don't want to migrate your existing images into the new software, what is prompting the idea to upgrade?