How to delete every other file?

[eugene7]

I have a folder where every file (.dpx images) are duplicated three times, with incremental file numbering.
I need to either extract every third file into a new folder, or delete the two duplicates (delete every other file, applied twice?).
Then rename with new incremental numbering.

Been searching most of this morning - but cannot workout if this is possible, or not?

[xnview]

do you have tried 'find similar' to remove duplicate files