If it's only a few images and you don't have $800 to spare for Photoshop, you could probably find someone who already has it and see if they'll scale them down for you.
If you'd rather do it yourself, GIMP is free and is pretty good, but all the functions can be a bit overwhelming if you're not used to using something like it.
Paint.NET is also free and does a decent job, and is easier to use too.
IrfanView is a very basic image editor and does all right. I think you said somewhere that you have it already.
All three will scale stuff down and have a way to "sharpen" an image if things get a little blurry, which depends on how much you're shrinking the image. GIMP and Paint.NET have a way to choose how much you want to sharpen the image, IrfanView does not -- you press "sharpen" it does it how it wants, no options.
And all are infinitely better than MS Paint. I tried taking a large image (2560x1440) and scaling it down to something manageable (800x450) and without sharpening it after, I think GIMP did the better job, Paint.NET second, and IrfanView third (it was clearly blurry). For all three, their own sharpen option cleared them up really well.
If you care, here is the
huge original, here is
GIMP's, here is
Paint.NET's, and here is
IrfanView's, all before being sharpened. If you open all the scaled one in separate tabs, you can flip between them and see the difference. Like I said, using "sharpen" fixed them all pretty well. Even without sharpening, there's not much of a difference.
I could do it for you if you want, using one of the three program listed.
