If you haven't set up automatic updating for Flash, you will have to find and download the update yourself, and the best place from which to pick it up is Adobe's official Flash page.
I'm reiterating this because there are web pages out there that spoof Adobe's legitimate one, and they are pretty well crafted (click on the screenshot to enlarge it):
But that thing that should give them away - if you're looking for it - is the shady URL (in this case: http://16.a[REMOVED]rks.com/adobe/). Also, clicking on most of the links apart from the "Download" button will reveal error pages - a sure indicator that something is very wrong.
Symantec researchers have analyzed the scam and point out that unfortunate visitors to the page are attacked from two sides.
"Option 1 is a pop-up message that requests the user to download a file named flash_player_updater.exe. Option 2 is the 'Download Now' button that requests the user to download a file named update_flash_player.exe," they say, and both contain the Ponik Trojan downloader.
Once installed, the malware proceeds to steal passwords from the compromised computer, then install either a piece of ransomware that impersonates the FBI or Interpol, or an ad-clicking component.