Need help from someone a little more computer savy than me, which would be most of you.

I can upload pics to the gallery, and can load pics from my computer while making a post/new thread. The problem is that all of my pics are just thumbnails. Sometimes that is all I need, but sometimes I would like them to be bigger. I have seen others post "big" pics with the thumbnail below. I just can't seem to figure this out.

I contacted 2 of the mods, 1 with no response, the other said he could walk me through if I was uploading from the gallery, but have had no other contact with him since.

So Mr/Ms. computer savy, please help the needy!!!!!