Selecting points in a given area

I've got a huge dataset, but only want those points which fall inside a certain area. It's too big just to go through the spreadsheet and eliminate the ones I don't want, so I was wondering if it is possible to do this using diva? I have managed to draw a polygon of the area I want, but am unsure what to do from here. I don't want to just remove the unwanted points from the GIS image - I actually want to remove them from the spreadsheet so that I can then carry out data analysis on the remaining points.

Thanks,
James