Normally, I'd first ask you which page do you want to add those images to (probably the Scenario Room page) and then I'd help you extend the article, figure out a good name for the image, upload the image and save the edit.
Unfortunately, image upload is broken.
If you want to try, you need to log in with a non-Steam account (you will need to make a new one if you don't have one) and then click this link: https://wiki.spiralknights.com/index.php?title=Special:Upload&wpDestFil…. It should bring you to the upload page with the file name filled in. I've selected a name that can be used on the Scenario Room page. Select the source file (your image) and upload it. You don't need to worry about the summary or upload options.
I'm 95 % certain you'll get the 403 Forbidden error, but you never know unless you try. One of the things that seem to cause this error is when you upload more than around 7 kB of data, which is a big issue for uploading images. Images smaller than 7 kB could work, but only icons could fit under this threshold pretty much. That's why image upload is broken.