If you have an editing programme,click on save as and follow the options.If its in "My Pictures "Highlight it ,click on Email this file,select make smaller.Reduced file will be attached to a new email which opens.
Microsoft photo editor should be available to you - go to the file, right click and choose 'open with......' and you shd see microsoft photo editor in the list. It has simple image re-sizing options under 'edit image', then you can save the ned product.