IPhone keeps saying storage is full?

Ok so my mom accidentally got me the iPhone 4s with 4gb & that's the lowest I was super upset but I was introuble and she got it anyways so I kinda had to deal with it, and I have dealt with it for months now but now all of a sudden it's telling me I can't take pictures because there's no more storage. I have just a few apps that I've downloaded and I haven't downloaded anything in a while. I was just playing a game and a notification popped up saying I need to check my storage. I have no idea why it's saying it's getting full when I haven't downloaded anything, and plus I only have like 4 photos in my phone. & 2 games and I think 7 downloaded apps. And another question is can I switch my phone for a different iphone? With no charge?

So yeah the iphone says go to your storaage and check usagage soo- do this: Press settings, then "General" then "Usage" then "Manage Storage". This will tell you what's taking up your space- (also text messages take up a bit of space)

No you can't switch to a new one for free, that's like swapping a ford for a Ferrari for free. You have to pay to get the upgrade.

@gotter is right. Settings > General > Usage to see what's gobbling up your space. Also, the lowest they made is a 8gb, not a 4gb. Your gaming content is probably one of the fattest ones on there. That and texts. Best luck.