Loading more articles into Content Magic
for more RSS feed posts. 

if you head to the content magic tab within the software, on that page you wil see the existing RSS feeds and a small refresh button on there - that will bring in new posts if they are available. 

shown here: https://www.screencast.com/t/QinPceD70N0 

If you want to go through the posts and delete or archive the ones you've seen to make more room

you can enter each feed (by clicking on the name in the previous step)
and then next to each feed article is a tick box and an Archive option shown here