How do i TRANSFORM AN IMAGE

[Digsee]

Hello

I have been taking digital picyures of paintings in order to post on my
website. Most are ok but the odd one seems to taper to the right ie not
exactly square. I have been shown that you can correct this using the
transform function on Photoshop. However, is there any free or existing
Microsoft programmes that can correct this kind of problem?

Am using Windows

Thanks

Digsee