I have a 550 watt power supply but it gets a lot of dust in it because I have a small case that is the Rosewill SRM-01, It doesn't get enough air. I have a a320m motherboard and a Rx 560 but I just want a bigger case
With mATX you're not going to find very many larger cases so you'll probably have to switch to an ATX case/mobo if you want something bigger. As for the dust in the power supply and the fact that the case doesn't have very much airflow is largely due to the fact that that case is budget and isn't build for big gaming setups or the like. You're going to have to spend a bit more on a case and fans for more airflow.