Working with audio or video can quickly fill up your hard drive!
You can either manually go through your project folders and in the Audio Files sub folder you'll find the files in that project.
You can open the Logic project and in the Bin choose Edit > Select Unused.
Then choose Audio File > Delete File(s)
if you wish to.
However, I would ALWAYS recommend backing up your projects to an external drive first!!! Either use time machine or just copy the project folders to the external drive.
You might also want to check that you're not saving ALL the assets to every project. i.e. In the Save As... dialog you can choose to save assets. Great idea to save external audio files to the project folder... but unless you're sharing your project with a collaborator or a studio who need them, untick 'copy exs instruments /ultrabeat samples to project folder'. This can save a lot of space!
btw, this is covered in the Logic 101 if I remember correctly.