I suggest you buy an external drive. The larger the better. A 2T drive will be cheaper than a 1T drive. I like the Seagate USB 3.0 Backup plus drives. Works on USB 2.0 ports. I don't recommend Western Digital because of the boot problem with some of their drives. In addition, WD drives and Mavericks have had really bad results with lost data. They come formatted for PC but easy to format in Disk Utility. (You can partition the drive into segments for additional options.)
Clone your drive using one of these free applications.
All your files will be safely backed up.
Use OmniDiskSweeper to clear up space on your internal drive.
You need a minimum of 10% free for the system. 15-20% is recommended.