macbook bought in 2007, how can i upgrade to os x mavericks?

No.

Your MacBook doesn't meet the system hardware requirements.

OS X Mavericks: System Requirements

To install Mavericks, you need one of these Macs:

• iMac (Mid-2007 or later)
• MacBook (13-inch Aluminum, Late 2008), (13-inch, Early 2009 or later)
• MacBook Pro (13-inch, Mid-2009 or later),
• MacBook Pro (15-inch or 17-inch, Mid/Late 2007 or later)
• MacBook Air (Late 2008 or later)
• Mac mini (Early 2009 or later)
• Mac Pro (Early 2008 or later)
• Xserve (Early 2009)

Your Mac also needs:

• OS X Mountain Lion, Lion, or Snow Leopard v10.6.8 already installed
• 2 GB or more of memory
• 8 GB or more of available space

You may be able to upgrade your MacBook to OS X 10.7 Lion

System requirements for OS X Lion and Mac OS X v10.6.8

OS X Lion system requirements

To use Lion, make sure your computer has the following:

• An Intel Core 2 Duo, Core i3, Core i5, Core i7, or Xeon processor
• Mac OS X v10.6.6 or later to install via the Mac App Store (v10.6.8 recommended); you can install without Mac OS X v10.6 by using an OS X Lion USB Thumb Drive, available on the Apple Online Store
• 7 GB of available disk space
• 2 GB of RAM

If your Mac does not meet these requirements, you will need to upgrade your Mac before installing Lion..

You can get a software download code by purchasing OS X 10.7 Lion here.

http://store.apple.com/us/product/D6106Z/A/os-x-lion