Hi jackeb, :~
I am NOT a computer wizard....I like nuts and bolts BUT...this is how I do it.......
Do you have access to 'Windows Paint' on your computer

If you go to a picture in your files and right click on it the computer will give you loads of options,in a long vertical list starting out with Preview,Edit ,Print ,Preview,....the 11th option down ( on my computer ) is just the word 'Open with ' BUT next to it on the right hand side is an arrow, follow that across and it should produce a sub-menu.
My 4th option down is simply entitled 'Paint'. Click on this option and you will probably find that the image that you now see is SO big that only a small piece of it will fit on your screen.
Across the top left is a horizontal list of options, which go File, Edit,View,Image,.....LEFT click on
Image and it gives you a drop down box of ...Flip / Rotate , Stretch / Skew, etc............ LEFT click on
Stretch / Skew.
This will produce a small blue headed windows box Headed...Stretch/ Skew. There are 4 boxes but you are only interested in the top 2
The top 2 are under the heading of 'stretch...and your cursor will be flashing next to a fully coloured blue box with 'Horizontal' next to it and 100% in it.......delete all the 100 and replace it with 50....then move your cursor down into the box below which is labeled 'Vertical' . Delete the 100% again and replace it with 50...then click the OK box and your image SHOULD shrink to fit in your screen, if it doesn't then shrink it again to say 80 in both of the Vertical and Horizontal boxes.....You can either save the image or go to exit and windows will ask you if you want to keep the changes and obviously you click on yes.
NOW when you try to upload the image it should be OK. I think that if it will all fit in your screen once it has been through 'PAINT' then it will upload OK to the site.
If it is an Image that you like your you want to keep then
copy it in the document / picture file first and ONLY alter the copy...that way the original is unaltered and Ok to keep.
I hope that it all makes sense to you, I have literally done it step by step on an image that I have so it should work out ok......any more problems just ask.
Alb.