Deciding which License Server/Manager to install depends on what versions of the software you are running.
Option 1: All of your Terrasolid products are 64-bit versions: install the 64-bit version of License Server/Manager.
Option 2: All of your Terrasolid products are 32-bit versions: Install the 32-bit version of License Server/Manager.
Option 3: You are using a mix of 32 and 64-bit versions: Install the 64-bit version of the License Server/Manager.
Note: additional steps are needed to enable your 32-bit TerraSlave on the 64-bit version of the Licence Server/Manager.