Using AMD Graphics card

I have recently installed Ubuntu 14.04 in my Lenovo Z51-70. It has both integrated Intel HD5500 graphics and AMD Radeon graphics card. But when I run the command "lshw -c video", its showing only Intel graphics. How can I switch to AMD graphics?

EDIT

Output of lspci -k | grep -EA2 'VGA|Display' is

00:02.0 VGA compatible controller: Intel Corporation Broadwell-U Integrated Graphics (rev 09)
    Subsystem: Lenovo Device 3824
Kernel driver in use: i915
--
04:00.0 Display controller: Advanced Micro Devices, Inc. [AMD/ATI] Venus XTX [Radeon HD 8890M / R9 M275X/M375X] (rev 81)
    Subsystem: Lenovo Radeon R9 M375
    Kernel driver in use: fglrx_pci

First install the latest fglrx driver if it is not installed.

sudo apt-get install fglrx-updates

and reboot.

You can switch adapters in Catalyst Control Center or in terminal

sudo aticonfig --px-dgpu

switches to AMD

sudo aticonfig --px-igpu

switches to Intel

aticonfig --pxl

shows status.