Mac OS X has fairly good memory management but it’s not perfect, and sometimes RAM can be held unnecessarily in the “inactive” state despite the contents no longer being needed. If you’ve been participating in memory heavy activities or you just need to free up some available RAM you can actually force Mac OS X to clear out inactive memory.
but, if you really want to free up your inactive memory try the terminal command: purge.
1.Open a terminal session on you mac
2.type the command “purge” and press enter….
a few seconds later your free RAM will be cleaned!