Question about Malware

I think Malware is still on my computer (after I hired someone to clean it).

I did more research on stuff and realized that jpgs and pngs could pose a threat. I deleted all the files on my computer and will clean off my external hard drive of all unneeded jpgs, pngs, and any double extension, jpg/png files....pdfs I will also delete.

Earlier, I noticed a few double extension images on my computer and deleted them. They're bad news and maybe the source of my problems. Which brings me to another question, can deleted files still pose a threat? I didn't use Bitdefender's file ripper... I just grabbed everything and pressed delete, and then emptied the recycling bin. (I'm still learning about internet security software so...)

I talked to someone about installing Glary Utilities, but the people at Dell say not to do that...(two file cleaning apps isn't a good idea).

I know how to work a lot of software, but there's still much to learn. Any help would be welcome.