How do I free up gmail space on my iPad?

I Have 1gb in use with my gmail account - how do I free up some of that space? Can I clear the cache on an iPad? Remove attachments?

tumblr also has 700mb in use. Can I only delete the app to regain this space?

I want to clear it up so I have room to add music, etc for vacation but right now it's full. I cleared it out to upgrade to iOS 8.1 about two months ago and now it is full again.

Seems odd, in retrospect, that apps have no way of clearing their cache. Wouldnt it's be great to have that option so it's only the app size and perhaps your personal settings can be minimalized and restore disk space to the user?