I have the licence for construct 2 and when i launch it from desktop works fine but when i launch through steam it loads free version how do i launch my full version from steam?
If you bought a license from the store here, then you are licensed for the non-steam version only.
Conversely - if you bought a Steam license, then licensing is dealt with by them and you would not be licensed for the standalone version that is downloadable from here.
The 2 versions are not interchangeable. A licensed version of one version doesn't allow you to have a licensed version of the other.