My website is starting to get some traction

I noticed ARZ Host specializes in dedicated servers and VPS. I’m currently on a shared plan, but my website is starting to get some traction. At what point should I consider upgrading to a VPS or dedicated server?

When either

A) your host complains that your website is using too many resources and doesn’t fall within your plan anymore, or
B) your website becomes really slow because the shared hosting isnt fit to handle it anymore

You should upgrade your server when the increased traffic is so much that it slows down the website and causes performance issues. You should also upgrade if you need more resources like CPU, RAM, or bandwidth.