You can locate the different account types by scrolling through the Market Watch pairs/instruments. If you can't see them/any, right-click on a pair/instrument and click "Show All".

Standard Pairs     $7 Commission         Majors pairs have a medium spread. 

Pro Pairs* (.pro)    $8 Commission         Majors pairs have a smaller spread. 

Var Pairs (.var)     $0 Commission        No Commission and higher spreads. 

Mini Pairs (.mini) $1 Commission        Smaller lot sizes (1 lot = 1000).

Big Pairs (.big)     $10 Commission      Larger contract sizes, depending on the pair selected.

*The above commission stated for Pro pairs is excluding which holds a commission fee of $10, as it falls under the Metals category. 

Different account types are only available for Forex and certain other symbols.