How to remove picture in Desktop Pictures Folder

I'm fairly new to my iMac...I've had it less than a year. Somehow (don't ask me how!) I've managed to get a couple of personal pics under the" Desktop Pictures" folder that is found when you right click on the desktop and select "Change Desktop Background". When it opens there are several folders under "Apple" one of which is "Desktop Pictures". The ones in question are pictures I'd previously used as my desktop background, but I do this all the time and none of the others have ended up stuck in this folder. I don't know how I did it, but I did and I can't seem to remove them. It's not a life or death situation and I can live with it, but to be frank they are pictures of an "ex" and I'd prefer to remove them if possible. Please advise. Thanks in advance for your assistance.