Which option are you pointing at"?
There are, when you have the latest drivers for that GPU installed, 2 options to use the GPU
1. For hardware acceleration of video on for instance the FX's that support that hardware acceleration, this option is normally automatic choosen by the program at Options/Preferences/Video, when the program recognise it as supported.

2. Using in some case the old Cuda-help at rendering with some codecs, that option has to be allowed in Options/Preferences/General