How to join

MultiMC

MultiMC is one of the best third-party launchers, especially if you want to use mods or hacked clients for older versions of minecraft
Download: https://multimc.org
To add a client.jar, click "Edit Instance" (Your 1.5.2 vanilla instance) and "Replace minecraft.jar". Use any client you wish.

Betacraft-Launcher

The betacraft launcher is the best launcher if you want to experience minecraft the way it used to be. No annoying crashes, no broken skins.
Download: https://betacraft.uk/downloads

Vanilla Launcher

Press the "New Installation" Button and select the current server version. Then select a different game directory by clicking on "BROWSE".
You can now make a new folder where the instance will be housed. Select the new folder and click "ok". Then click "Create"