Getting a higher voltage from a battery than specified
As m.Alin suggested, you could you boost regulators. Look at the following example from LTC



You can input your input and output parameters and regulator suggestions will be provided.

Choose the best one that suits your need.

Here is a schematic of a boost regulator, one of the cheapest regulator chosen from the list.



Another power products manufacturer is TI. You can use their webbench (online software) to adjust lot of parameters and choose the best regulator for your needs. TI products may be cheaper than LTC.





Edit:
If your requirement is one off only, then you may go with Jippie's suggestion and look for a ready built boost regulator. Pay special attention to the wattage as some of the cheap modules do not include a heatsink. They expect the user to add a heatsink for prolonged operation.