When I had my first website I was advised to download Irfanview. It is really easy to do.
Irfanview.Softwarecenterz.com
After you download
Find the pic you want to change and right double click and find open with on the menu and choose irfanview.(the guy who created this is named Irfan) It will take you to an Iranview window and you will see your picture in that window. At the top you will see:
file edit image options etc
choose image and click on it find resize on the menu and click on it then you have the option to change it to half the size or you can choose what size you want it and click ok. Then you will see what the size you chose will look like- then save it in the file you want - And you are done.
If your pic is too big to see then I resize it to half and click ok then I can see the pic and can edit it to crop or whatever you decide to do.
I have learned to use the Enhance colors on the image menu. It isn't hard so experiment and you won't lose your original file so you can redo as many times as you want. I have found if you move the gamma slide to the left just a little it will darken the pic a little and improve faint looking pics or go the right to lighten a dark pic. It is really easy!
There are alot more options you can do on it I just know how to do the ones I need.
It operates pretty much like using microsoft word or works.