Execute the setup and follow the instructions, it is not required to first uninstall a previous release.
bouml.exe is compiled in static mode and only require mingwm10.dll installed by the setup. To save place the other executables are compiled in dynamic mode and require all the dll installed by the setup.
The installation mode depends on the distribution, it is indicated it in the page download
By default the executables are installed under /usr/lib/bouml (debian based distributions, or 32bits redhat based distributions) or /usr/lib64/bouml (64bits redhat based distributions), and the shell script bouml is placed under /usr/bin
The shell script bouml must be used to start BOUML, it sets environment variables allowing it to find the plug-out.
The installation is done through the finder (see this video on YouTube).
I encourage you to create a folder bouml under Applications to install bouml into and to also to extract in it the tar of the Plug-out projects and the one of the translation files.
Through the finder double click on the dmg to install, a new window will appears containing the icon of the corresponding application, drag and drop this icon into Applications or the sub folder you created.
Now you can close the window and the pseudo disk added in the finder by the installation.
To start bouml or projectControl or projectSynchro you can use the finder, or the launchpad (you may have to use the horizontal arrows to go into the screen showing their icons), and obviously you can also add the expected application(s) into the dock.