Skinny guy

It's easy, just go to your profile, then click the little gray square button by your profile pic, then you can select another picture saved on your computer/phone whatever you are using.

I tried it says file size too big?

Ah, no trouble there.  On your computer, go to the folder with the picture, click the picture just once, then click it again using the right button on your mouse/laptop touchpad.  you'll see a menu open up, scroll down the menu to the "open with", a flyout menu will then appear - select Paint.  The picture will open in a program called paint.  In the upper left corner of the paint app is a button that looks like an old 3.5" flopppy - click that, then select save as.  Type in a new file name to save the picture as (so you don't mess with the original picture).  Click the "resize" button in the upper left area, a dialog box will open, and you can resize by percentage.  Notice there is another option to resize by pixels.  I'd use percentage (try 30% for both horizontal and vertical), then click OK.  The pic will get smaller.  Keep doing this until you get the picture down to about 260ish x 260ish pixels.  That should be the right size for the profile pic, that's what mine is.

If you have trouble, just send me the pic and I can resize it for you.  Happy to help.