Try logging into the computer as an administrator. The Mac does not let you modify the /Applications folder unless you are admin.
There is also the Nyquist brick wall limiter here Peak Limiter . See here for how to install Nyquist plug-ins: Missing features - Audacity Support . You will still have to be an administrator to install it. If you have an IT Manager ask him or her for help.
Hard Limiter is partly a distortion effect so is not recommended for your purpose.
I also suggest using Audacity 2.0.5 instead: Audacity ® | Download for Mac OS . You can install it to your own Desktop if you prefer then the Mac will let you modify the Audacity folder.
Gale