You will be presented with a list of all the mems you have created so far. Look for the mem you want to edit and then hover over it. A pencil icon will appear as you hover over the mem, click on it. Now you will be able to edit your mem, afterwards do not forget to click save!
Create a mem
Points given for mems
Delete a mem
Embed Video or Vine in a mem
To help you understand the difference between image courses, courses with images and mems read these articles:
Create an image course / create picture course
Add pictures / photos to my course