Low Memory Usage When Rendering - From 80% to 25%

While rendering a project, the amount of RAM used was normally 80% of 8GB. However, that number has now dropped from 80% to 25%. I have not adjusted any settings so I don't know why there's a decrease in the amount of RAM used. Please let me know if you have any ideas. I've only been using this program for 1 week - newbie.

Thanks,

James