Pick the group that matches your board. Binaries are served from the Bitdsk_Miner_Archive repository; sizes and SHA256 checksums are listed here so you can verify what you downloaded.
.zip — upload it in the miner web UI under Settings → Firmware, and your settings are kept (on U1/U2 the CD KEY too).
Rows marked Abandoned or Expired are kept for reference only — do not flash them.
For a board that will not boot, use the browser flash tool instead.