Day by day, your MacBook will store some information in the system cache such as system logs or big file cache for a faster startup, but in the long term, they become useless and only take space in the hard drive. To free some space in memory, you can access the folder that contains all these files and delete them:
Enter in the Finder
You can quickly access the folder pressing the Command + Shift + G combination and copy/pasting the path.
This will help you free up lot of space by deleting junk.