That "utility" is showing 155 GB space used by what it calls "Large & Old Files", not all the space used on the drive.
And clicking on that item (as your screen shot shows) it appears that the utility thinks that you have "movies" that take up 116.8 GB of space on your drive. You could start there by clicking on Movies, which should show you a list of various movies/video files that are stored on your drive. You can delete some, or all, of those. I don't know if the utility simply puts those in your trash, and you need to empty the trash to actually get rid of the files... or, it removes those files directly, and you are done. That will get a lot of your free space back.
But, how much space do you need to free up? If your storage drive is 256 MB, then I suggest that you should have at least 15% free space (just my opinion), or at least 10% free space in normal use.
Finally, as suggested above, the Macbooster utility can be deleted, and you CAN use a utility that is known to be useful (and safe), such as the mentioned "Daisy Disk", which will actually be helpful without needing to pay for that help.