Apps that refresh data on the web usually have a menu setting to adjust the interval. So you could open an app like Facebook, go to its settings, and adjust its refresh rate to every 30 minutes, every hour, etc. There's usually a Never or Manual option, which will turn off the app's automatic refresh, and require you to manually refresh the app.
But that really won't solve your problem if you have too many apps installed, because any time you try to refresh one of these apps (even manually), you might get this low memory warning. That's why I suggest uninstalling any app that you really don't use.