Deleting plist & dlist files

Good day!

I have a series of *.plist & *.dlist files that have been backup to my external drive and am trying to delete them, but I am prevented from doing so. I have tried different methods to do so, but they are designated as being that the files are locked. They are listed as "SQ_{and a 32bit address}.plist/dlist" and are dated from several months ago. Although they do not seem to take up much disc drive space, I want to clean up my attached storage drive. Are the files of days gone-by necessary and if not, then how do I rid of them?

Thank you,

Eric