How to enable amd discrete graphics card?

I bought a new laptop, and have a problem with graphics card driver. I've been trying to fix problem for few days, please, help me if you know the answer.

Hardware: Dell Inspiron 15 3541 with A6-6310 QUAD-CORE with Radeon R4 Graphics. 4GB Memory. Discrete graphic AMD R5 M230 2GB card.

OS: Ubuntu 12.04 LTS

For now, Ubuntu says that I have only 3,3 GB of RAM. As I understand other 700 Mb are used by enabled integrated AMD R4.

I want to use discrete card with its 2 GB of RAM and use all of my 4GB RAM.

I've tried to install proprietary drivers from AMD site. But Discrete card still doesnt't work and invisible.

The output of lspci -k | grep -EA2 'VGA|Display' terminal command:

00:01.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Mullins [Radeon APU A4-6000 with R2 Graphics]
Subsystem: Dell Device 0658
Kernel driver in use: fglrx_pci
--
01:00.0 Display controller: Advanced Micro Devices, Inc. [AMD/ATI] Sun PRO [Radeon HD 8500M Series] (rev ff)
Kernel driver in use: fglrx_pci
Kernel modules: fglrx

I would really appreciate your help. Evgeniy.