Q: What is the latest version of OS I can run for a Macbook 4,1

Currently running OS version 10.5.8. What is the best version based on my Macs capability?

How do I upgrade now there is no automatic upgrade from Apple?

Here are my specs

Hardware Overview:

  Model Name:    MacBook

  Model Identifier:    MacBook4,1

  Processor Name:    Intel Core 2 Duo

  Processor Speed:    2.4 GHz

  Number Of Processors:    1

  Total Number Of Cores:    2

  L2 Cache:    3 MB

  Memory:    2 GB

  Bus Speed:    800 MHz

  Boot ROM Version:    MB41.00C1.B00

  SMC Version (system):    1.31f1

Thanks