Samsung Galaxy Grand is running out of space

I'm using a Samsung Galaxy Grand and I have not much apps installed: in fact just about 3 apps besides the pre-installed apps, but still I have no space when I'm downloading apps like Skype and Candy Crush. On the process of updating my phone I get this message, that there is an insufficient space; the phone too shows a lot of used up space. I have an 8GB microSD card, which is hardly used. Please help me on this.