There are several things you can do to reduce the size of the installation.
1. You can remove skins that you are not using.
2. You can remove setup and upgrade scripts for databases you are not using. mojoPortal supports 5 different database platforms and we include setup and upgrade scripts for all of them in the deployment package so that you could switch platforms just by changing the dlls for the data layer. The majority of mojoPortal users are using MS SQL, so you could delete the scripts for MySql, Firebird, pgsql, and SQLite. The scripts are located at:
so you can delete the ones that do not correspond to your db platform.
4. If you don't care about supporting languages other than English you could also delete translation files for other languages. There are localized files in the /Data/HelpFiles folder and in the /Data/MessageTemplates folder. There are also file in the App_GlobalResources folder. Note that the English files are named like Resource.resx and BlogResources.resx whereas other languages are identified by a language code in the file name like Resource.it.resx for Italian.