M-g runs `gnus-summary-rescan-group'

`gnus-summary-rescan-group' is an interactive compiled Lisp function
  -- loaded from "c:\Program Files\XEmacs\xemacs-packages\lisp\gnus\gnus-sum.elc"
(gnus-summary-rescan-group &optional ALL)

Documentation:
Exit the newsgroup, ask for new articles, and select the newsgroup.