Album art is either embedded in the song, or a separate jpg file in the same folder. Assuming it’s embedded, then many MP3 software program will allow their removal. WinAmp: load song to play, press Alt-3 to bring up ID3 tag. One of the tabs will allow removal.
A faster program is MP3Tag which allow batch processing. Open it to the MP3 folder, select desired (or all) MP3s to be stripped, right-click, select Extended Tags. Once there, click on the red X to the right of the album art placeholder image. Click OK. This will remove album art from those selected MP3s.
Note: There is no undo in these programs. If you are unsure about what you are doing, make a backup copy of the songs. Also, embedded art, depending on the graphic size, usually aren’t large enough to make deleting them a worthwhile option if you want more space.