There's not enough info; but it usually works like this.
5.1
Speaker quality
Subwoofer quality
Room treatments.
If all those are perfect, then we can talk 7.2 or Atmos; but for 99%, one of those 4 is still the best spot for improvement.
The receiver just needs to do whatever you need done. Decode 4k, power 7 speakers, whatever. You won't notice a sound improvement through a receiver change.