Piece of cake. Read up on ACTIONS and BATCH operations in your manual. I do this all the time, converting big PSDs to med & small JPGs.
As to not having an option to save….bizarre. If there are PATHS in your file, that might be the problem. But if you FLATTEN layers and kill all paths, RGB mode, you should be able to save as anything. Also, SAVE COPY might allow you.
Try your BATCH ACTION first on a small, temp directory–, sometimes it’s tricky to understand the saving options.