How to use TechTool in PPC's and IntelCore?

I have a question about upgrading. What is the right thing to do in my case?

First the history. In 1999 I purchased TechTool 3.0. for iMac Power PC G3 OS 9.2.1 both, run perfect to this day.

In December 2003 upgrade to TechTool 4.0.1 for eMac PPC G4 OS 10.2.11.
In 2010 upgrade to TechTool 4.6.2 for the eMac was upgraded to OS 10.5.6 This is also still running perfect.

In the meantime next to iMac/eMac PPC's there are in use an iMac Intel Core i3 with OS 10.6.8 and a MacBookAir Intel Core i5 with OS 10.9.5
For the latter two I like the compatible version of TechTool.

Question: Which version do I need and can I upgrade or do I have to buy a new version?

Regards,
Hubert.