It depends. There are a few factors dictating the amount of RAM you should have. These include the intended purpose of your site or server, the amount of traffic you normally receive to your site, how many plugins you decide to use, and how many websites you plan on running through your VPS. 512MB of RAM is enough to host a simple website. However, if you want to run several complex websites or a gaming server, you should be looking at at least 8GB of RAM.