Download and install the Mac OS X 10.6.8 Update Combo v1.1 update. Open App Store on the Dock or in Applications folder. Sign in using your Apple ID and password. Locate the Lion installer then purchase and download - $30.00.
Taken from Apple Website....
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.
In other words, FIRST UPDATE your system to 10.6.8.... 10.6.8 will install the MAC APP STORE on your computer.. SECOND.... Buy Lion from MAC APP STORE (you may need to create an Apple Login and Password). THIRD... Launch the LION installer and follow the on-screen instructions. Made sure to install ONLY THE COMPONENTS, don't ERASE your system before install. This way you don't lose your data (pictures, music, documents, etc.)