CentiLeo is distributed as an archive via Download page. This archive has several folders for different Cinema versions. Each folder has all necessary plugin files and should be copied to the Cinema plugins folder.
Extract downloaded archive
To install CentiLeo for Cinema R21 you should copy CentiLeoR21 folder from downloaded archive to the plugins folder of Cinema 4D, e.g. to “C:/Program Files/MAXON/CINEMA 4D R21/plugins/” (or other custom plugins folder).
For older Cinema versions use the other CentiLeoRXX folder copy.