The "why" and "should I" questions are much more difficult to answer, especially positive.
In fact, most businesses won't do it on their PC's and most consumers, I think, won't do it either.
Upgrade to Windows 8 Pro till 31st of January 2013 is available at very low price $39.99. You will have to pay more for this after this month.
Follow the inline steps to upgrade to Windows 8 Pro:
1. Go to Microsoft official website >> log in and click on Upgrade to Windows 8 Pro section to install Windows 8 Upgrade Assistant.
2. After Windows 8 Upgrade Assistant is installed, run it to purchase Windows 8 Pro.
3. Go through the on-screen instructions to check if it is possible to upgrade to Windows 8 Pro in your PC.
4. When it is finalized that your PC is capable of running Windows 8 Pro, follow the on-screen instructions to make payment and subsequently download and install your OS copy.
5. After the installation is complete, customize it as per your preferences.
Note: You can only upgrade to Windows 8 Pro, if your PC has Windows XP SP3, Vista, Windows 7, Windows 8 Customer Preview or Windows 8 Release Preview. In case of XP SP3 & Vista, you may need to reinstall the apps.