About this Mac shows wrong graphics on Macbook pro 15" late 2011 When I check out the Graphics on 'About this Mac' it says that it is using the Intel HD Graphics 3000 384 MB even if I also have an AMD Radeon HD 6750M. Also when i click on 'Displays'-tab, i see the Intel HD Graphics 3000.

I am note sure which one is used, and how do I change so the right and better card is used?

I am using OS X Mountain Lion on a Macbook Pro 15" late 2011.
You could try using gfxCardStatus which will show you in your menu bar which chipset is currently active and let you specify one or the other.
Current MacBook Pros dynamically switch between their two different graphics chipsets depending upon system load and currently active application; for example, the tech specs page of the current MacBook Pro lists the following:

Intel HD Graphics 4000
NVIDIA GeForce GT 650M with 1GB of GDDR5
memory and automatic graphics switching