In the box on the right hand side you are given options to alter your picture including

brightness, colour, rotate and flip, cropping, red eye removal and at the bottom,

'Change picture size'.  You can try these later.

To compress your picture select COMPRESS PICTURES

·        Click Compress Pictures

·        In the ‘Compress For’ list on the right hand side, select DOCUMENTS.

(NB the EMAIL option reduces the file size to a level that seriously effects
the quality of your picture, reducing it to a DOCUMENT level is usually
small enough for it to be sent via email.)  

You will see at the bottom of right hand box that it shows you the old and

the new file size

·        If you’re happy with this, click OK

IMPORTANT

    Now you need to save this version of your picture HOWEVER, it is best
    to keep your original picture in its original uncompressed quality, in case
    you need it for any other purposes.

    To do this, click SAVE AS and add a ‘c’ letter at the end of the file name

    to create a different name to the original file and to indicate that
    this is the compressed version