Upgrading my wife's PC

My wife's computer is struggling. I'm wanting to cheaply upgrade this so she can play games like The Witcher, The Witcher 2 and Sims 4. I'm wanting to keep the tower and only replace the essentials. Thanks in advance for any suggestions! I can't afford to replace the whole thing, so please no "buy a new computer" responses please! I just want her to be happy with her games again.

• eMachines ET1331G-03W LINK