FortiGate Anti-Spam upgrade

[AciidSn3a3kr]

We have a FortiGate 100D appliance as our firewall. 

It currently runs 5.2.4 build 688 firmware.

As of recently we have been seeing increasing numbers of spam.  Since we're running an old build, would I see any difference in the anti-spam capabilities, could I potentially see a reduction in spam? 

Either way, i'd like to upgrade for security reasons. But I would simply like to know if the spam detection is different in 5.6 than in 5.2?

Thanks