Is there a way to save messages but delete them off the iPhone?

Hi, I have an iPhone5. Recently I've been texting a lot and realised it takes up a heap load of my memory (so far about 2.5GB in just a few months). At this rate I'm going to fill the 5GB left.... I have used SMS but mostly iMessages. I was thinking of deleting them directly off the phone but some conversations I want to keep... so I was wondering if there's a way to store messages but delete them off the phone? Atm the version is 9.0.2.
I do also own a MacbookPro and my messages seem to be syncing to the Macbook and I've heard you can delete off phone and it'll store in the Macbook still. I haven't tried it yet in case it doesn't actually save..

Just making sure, is there a way to save the dialogue as is but just off the phone so it doesn't use up all my memory?