You should have the Paint programme in Accessories section. Maximise the Paint window. Choose File>Open and select the picture which you have already put intoa folder. Assess what % you wish to reduce. Choose Image> Stretch/Skew, type into the top two boxes the % you want to try. Click OK. The image will now be resized. You can go back to resize it. To save it, choose File >Save As and in the Save as type box choose JPEG. Type a new name for this picture. Close the Paint programme, write your e-mail message and attach your new picture.