drop doqn options on store

[anzagi]

Hi all, I am new to this and am looking at it for someone else

 

you can see here http://www.brandsclothing.co.uk/heavyweigh...c006-p-319.html the size dropdown, well the person I am looking at this for would like to be able to select more than one item at once even if its different sizes such as http://www.polo-shirts.co.uk/Hi-Vis+Safety...y+Green+T-Shirt

 

could someone point me in the right direction please? I don't mind having a look but don't know where to start

 

Many thanks in advance