Microsoft makes all carriers have their Apps configured so they can be deleted. This gets rid of all but the most basic core Apps. What you don't need, don't use.
Never expect more from a device than what you are paying for. A Lumia 520 will NEVER be a Lumia 1520 or HTC One (M8) for Windows.
In Android it is different. In iOS it is different. In FireFox OS, Ubuntu Touch, Sailfish, etc.: it is different. Operating systems behave differently. This is exactly the reason why there are different OS choices; a different design philosophy. Wishing one to be just like another is actually wishing that OS to disappear...
http://developer.nokia.com/community/wiki/How_to_free_storage_memory_on_Windows_Phone
But that does not free RAM. Preventing Apps from running or continuing to run in the background will free up RAM.
Use multitasking view. Hold the back button and close any Apps still running that you don't want active.
Do a periodic Soft Reset to clear system memory. Hold the Volume Down + Power buttons until the phone vibrates and reboots (about 10-15 seconds).