probook 450 upgrade windows 7 to windows 8

I have just bought a Probook 450 G1 with Windows 7 Pro installed.

What is the best way to upgrade to Windows 8 Pro from the DVD provided?  I work from home so the higher security options not necessary.  The HP support site gives two options - inplace upgrade and clean installation as below.

http://h20566.www2.hp.com/portal/site/hpsc/template.PAGE/public/psi/upgradeMigrateDisplay/?sp4ts.oid=5405421&spf_p.tpst=psiContentDisplay&spf_p.prp_psiContentDisplay=wsrp-navigationalState%3DdocId%253Demr_na-c03451712-3%257CdocLocale%253Den_US&javax.portlet.begCacheTok=com.vignette.cachetoken&javax.portlet.endCacheTok=com.vignette.cachetoken

Also where do I find the Windows product key?

Thank you.