Image Sizing

Ok......I have literally lost my friggin mind! I have been figuring out alot of things I can do on the computer that I never thought I would even try, BUT, I need to somehow find a way to change image sizes and that my friend is not easy for someone who can't copy and paste. Yeah, I know it's supposed to be a piece of cake but for some reason I can make my own business cards but I can't do that! I am going to be researching a camera that will take photos up to 3800x2400 at 300dpi, so if any of you have any suggestions without me selling an arm, I would love to hear about it! That would eliminate a ton of the issues I am having right now. My etsy shop is up and running, real estate has picked up tremendously and lo and behold, I decide that I just have to open a store on Cafe Press! That's where I lost it......love the site, but, it's not near as user friendly as etsy is in editing and even adding items. I have a long road to hoe on this deal.......would somebody please stop me!!!! Off to paint.......much better at that!