Your computer CAN go to 10.7, but no further, according to this document:
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 [no longer available]
- 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.
To obtain 10.7 Lion, you will need to CALL the Apple Online store and purchase a download code they will email you in a day or two.