In selection interface, changing the structure is easy. Select a part of the protein and click on the button L,K or J. When you download a protein puzzle from FoldIt, they will sometimes be a collection of helices (spiral fat balloons), sheets (flat tiles) and loops (thin tubes). These "secondary structures", as they are called are not "real", they are just a convention used to depict certain common structures regularly found in proteins. The game allows you to override those choices of secondary structure and force them to be shown as something else instead.