The pics are easy and anyone can edit. Ex:
Click “edit” in the right column and find a line like this:
| [[File: Singleplayer.png|120px|link=Black Mesa: Singleplayer|Single-Player]]
Singleplayer.png => name of the pic
120px => size
link=Black Mesa: Singleplayer|Single-Player] => link to the wiki article, where “Black Mesa: Singleplayer” is the name of the article page on the wiki, and “Single-Player” is the way you want to show it as a link.
Just change the “120px” with a smaller numbers and the pic shrinks. Don’t forget to click on the “show preview” button before save changes, to see how it will affect the page.
But before shrink the pics, I guess is necessary a bigger font for the wiki. But I don’t know who can do it.