To determine the version number:

1) Go to the Pocket Tunes Search tab
2) Enter "pt://build" (without the quotes) in the search window
3) Tap "Search" on the keyboard

Pocket Tunes will pop up a window showing you the version number you have installed. The first three numbers arre the important ones. Compare those to what Apple says on the Pocket Tunes product page to determine whether you have the latest version. iTunes should also tell you if you have an update availabel for Pocket Tunes or any other app you have.