There's a big button at the top of the page linked that says "Download Now" or in the top article there's a link at the bottom of the "Microsoft Safety Scanner" article.
This tool will identify most common infections that are running on significant numbers of computers running Microsoft Operating Systems, and will remove most things it finds.
2. No search or removal tool is perfect, so after scanning for the presence with the above tool you should go to Microsoft Malware Removal Tool, download and run that tool.
The Malware Removal Tool is even more specifically targeted at malware that has found to be among "the most common dangerous threats." There is significant overlap between the two scans, but there are enough differences that it's a good idea to run both of them if you have reason to believe you might be infected.
Since you have been sucked into a SCAM, you do have good reason to believe that your computer is infected.
Note that both of these scanners need frequent updates, just like any other protection software, so although you can download them to run later, or to run again later, you really need to get a new download of the latest version if the one you have is a week or more old.
3. It would be a good idea to get an independent scan for infections from one or more of the reputable Antimalware sellers. Nearly all offer "free scans" somewhere on their websites that you should find with a simple search. Nearly all that you're likely to recognize are reliable and safe to use, but all have some differences in what they detect. Generally, none of these free scans will remove anything, but you should be able to trust them if they tell you that there are significant threats on your computer. If they give you a name for something they find, you need to make a note of what it is so you can look for removal instructions specific to that threat.
Symantec (a.k.a. Norton), McAfee, Kaspersky or a few others would be good choices and you should be able to search fairly easily on their sites for appropriate scanners.
4. You should have antimalware protections on your computer that you trust enough to yell BULLSHIT any time you see a popup, embedded ad, or receive an email or phone call claiming that "You Might Be Infected;" but finding the one you can love and trust is about like finding a mate for your ugly stepsister (And the first one you think you found might be a serial killer). If you don't have reasonably good defenses now, you'll want to get started soon, since it ain't all that easy living a safe life – on the web or anywhere else.
NOBODY you don't know well EVER calls you on the telephone or sends you email "because they want to help you."