Hi mate. Nice work. Handy having some panel beating/painting skills when takin on a task like this!!

To downsize images, this is a really easy program to use. And free.

Go to http://www.irfanview.com/ and download the free program.

Then open it, go to FILE - open, and pick a picture.
Then go to IMAGE - resize/resample and pick a new size then save it.

easy peasey.