MicrostockGroup

I can't figure it out.

Wait until you have to add categories, now that's freaking confusing.

Once you upload a picture, under the my files section, click on the blue and white arrow next to the image, scroll down, there will be two side by side boxes.  Type your keywords into the one on the left, seperated by commas, and then click the add button between the two boxes.

If you've already processed them you can't. All you can basically do is rearrange those keywords...so before you process those files on-line be sure you didn't miss spell or forget keywords because if you did you have to go through the painful process of deleting and reuploading. 
You'd think they would have figured out a way around that by now since they are trying to be more like the bigger sites with their "rejections ratio"