Since this is the office.misc newsgroup, I'll go out on a limb and assume
you have Office, which would include either Microsoft Photo Editor or
Microsoft Office Picture Manager (the latter for the 3 most recent versions
of Office). Both of those programs allow you to resize pictures in a variety
of ways.
Display the pictures using Office Picture Manager, for example, then choose
File - Export. Set the location as desired (not in the original location
with the original names if you want to avoid overwriting the originals). Set
Export using this size to Web Large or Web Small, then click OK.