You can upgrade to Windows 8.1 for free via the Windows Store. Just search "Store" on your system and it's the first result that will come up. Go in it and upgrading to Windows 8.1 is like the first option they give you. Do it. This is assuming that you have a legal copy of Windows, and not one activated with the KMS.
What was your last known malware infection ?
I suggest you to add Malwarebytes as an On-demand Scanner, it never hurts.
I also suggest you to add HTTPSEverywhere, Web of Trust (WOT) and NoScript, Ghostery to your Google Chrome extensions for better privacy/security.