Not sure what you can tweak because i haven't looked properly, but get 2x8GB of ram, it should be cheaper and gives you room to upgrade.
You'll probably get better answers if you post what you plan to use the computer for. Gaming? Video editing? 3D rendering? Productivity?
Improve it how? It helps to know your budget and what you're gonna be doing with it.
For just gaming an i7 isn't necessary. Neither is 16GB of RAM. The ASUS ROG series are way more than you need too as all Z97 Asus boards should OC the same. The H55 is crap. Get an H100i, Kraken X61, or Noctua NHU-15S. You don't need all SSD storage. Get a 120 or 240GB boot drive and a couple of 1TB HDDs. Dual 980s are stupid. The 980 is stupid. You are paying over $200 more for a card that is only marginally faster than the 970. I'd get one 970 or if you're crazy two. But not a 980.You don't need 750W either.