How can I delete all of my inbox messages in my Motorola E8 cellphone?

I have a Motorola E8 or better known as the model number E815. I want to delete all of my inbox messages because my memory is low, but I can only delete all of my outbox messages. My inbox doesn't have a erase all messages button like the outbox does. Is there a way to delete my Inbox messages all at once instead of one by one?|||Just read the manual that came with it, Or call your service provider. ~