If it is a Spry validation that is applied to the element then you should be able to select the element and see a bluish colored tab around the element. If you click on this tab it should bring up the properties for it in the property manager. You can adjust the formatting or the other values. You could remove this validation from the page completely by removing the event that triggers the validation and also removing it's Spry line of code in the page.
If it is a server side validation then you can remove it by editing the server validations entry in the server behaviors tab.