You can do it several ways. If you have Microsoft paint you can do it there, and also just upload it to photo bucket and you can re-size any picture there and then use the codes to get it on the site.
If you have a picture on your desktop, right click on it and it will open a menu, go down "open with" and then down to paint. It will open it up in the paint program for you. Depending on the operating system your using be it, Windows XP, Vista, or Windows 7 there is a re-size option at the top of the window. You open that up and select the % change you want to do. If you put in 10% in both the width and height boxes it will reduce the picture by that amount and you can continue to do that until you get it small enough to fit for your profile picture. Once you get to the size you want go up to the top and file save as and select as jpg to your desktop.
Then go to your settings on CDC and go to profile picture and select upload from computer, hit browse button and find it on your desk top click open and it should load and then select ok or save after that.
There are many ways of doing it though. Just depends on you and what you feel comfortable with doing. If you need help just send me a PM with your number and I will give you a call and talk you through it if you would like. Good Luck