Either boot from an external drive and access the internal hdd that way, or just take your time, if the internall hdd is full there's no other easy fix than deleting some stuff. Unless you want to ditch all your data and install a new internal drive that is...
lightroom keeps secret duplicates of each photo so they take up way more room. I'd only keep copies in lightroom of ones you are actually going to edit. There's a program called OmniDiskSweeper which is free and good to showing you how big each file and folder actually is.
Either boot from an external drive and access the internal hdd that way, or just take your time, if the internall hdd is full there's no other easy fix than deleting some stuff. Unless you want to ditch all your data and install a new internal drive that is...