Assuming it's the same as every other Marui with a front sight block I've ever had, you can just knock the pins out and remove the front sight block. Once that's off it's a simple case of unscrewing the barrel nut. Shouldn't be any need for a new outer barrel unless I'm wildly mistaken, unless the OP is simply more comfortable not having to do any of the aforementioned.
Edit: I'm aware saying 'just' and 'simple case' is very easy to say when you've done it multiple times. But there are a decent portion of resources to guide through the removal of a front sight block out there.