When you have set up your RSS feed for your blog, and click to view it, often you will notice that your recent posts will be listed a full posts or summaries. There are pros and cons to both.
The major one is that if you have a full post listed in the RSS feed, the reader probably will not visit your blog. The other end of that is does the summary say enough to get them interested to click through.
But if someone has recommended your set it one way or another, simply go to your sidebar menu in your dashboard, click on > Setting > Reading and you will find the spot to change that. Also, you can choose how many posts are listed in the RSS.
NOTE: Some people misunderstand this and think this the setting for showing full post or summaries on your blog. It’s only for your RSS feed.