How Do I Delete Low Bit Rate Songs From My Library

I really, really screwed up.....I was ripping a lot of CD's into my computer and I must have hit the wrong button....I accidentally added about 4500 low bit rate (between 150 and 160 bit rate) duplicates onto my Windows 7 music library. They show up in my J River Library as well.....How can I delete them without individually clicking on each song? Any help would be greatly appreciated. TY!