how do i upgred to mavericks ?

Back up your data, open the Mac App Store and try downloading it. If your computer's incompatible, you will be told so and the download won't be allowed.

If desired, append the last three characters of the computer's serial number to http://www.everymac.com/ultimate-mac-lookup/?search_keywords= and load the page; this will reveal what model it is.

(103845)

Apple Menu > About this Mac > More info button…

The model name & identifier will be listed in the hardware section of the report.

Supported models are shown at …

http://www.apple.com/osx/specs/