Most formatting options for an object, including number formatting, is available from the Properties tab on the left hand side of the client.
The default number format for any measure has been determined on the database level, but you can change this format to any other numeric format. The number formatting dialogue box provides a list of predefined number formats.
In case you need an advanced or user defined format, you can achieve this by going into Advanced format options.
Actually, the Advanced format option lets you specify different formats for positive, negative, zero and empty numbers, but if only positive numbers format is specified, this format will be inherited to the other numbers.