Ubuntu keeps a system cache to load the application fast. It saves your time but sometimes it heavily utilizes your system’s memory. You need to clean system cache to make System fast and to make proper use of System.
There is a separate tool available for this task. You need to download and install a tool called Ubuntu Cleaner.
sudo add-apt-repository ppa:gerardpuig/ppa sudo apt update sudo apt install ubuntu-cleaner
Now you can run the ubuntu cleaner by searching through the Unity Dash.