Need help installing win8 on second partition

Here's my situation.
I bought a new laptop (HP) which came with an OEM version of 8.1

I have a retail key and tried to use the 'change key' facility to use it instead of the OEM one - with no success, it was not accepted.

So I split the drive creating a new partition and tried to boot to my Win8 install media - but the laptop won't boot to the dvd even though the bios has the internal DVD set as the first boot option.

Can anyone assist with guidance as to how I proceed.

Thanks

if it came with windows 8.1 and you want to upgrade to windows 8.1 pro

control panel > add features > already have key

Thanks KYHI.

I found that option and tried it just before you replied.
It took about 2 hours (slow internet connection here) to upgrade,but it did the trick.

Now I have to call MS to activate it - "it has been used on a different computer".

Thanks again.