Running Shoes

Dear fellow runners: How do you know when to replace your running shows? I’ve had the same pair for the past two or three years because I don’t run all that often. I bought a new pair (basically the same as my current pair but with a different color scheme) last summer when Paragon Sports was having a huge sale (so they cost about $30). 

My current shoes have a tiny hole on one side but that’s basically the only thing I can see as being wrong with them. For all I know though, the bottoms are completely flattened out and not ideal for running (I’m making this up but it sounds like something that could be a thing). Here’s a photo of the bottoms:

To all the educated, experienced runners out there, how do my sneakers look? Do I need to toss them?