Usually it makes the most sense from a sound performance and financial perspecive to replace the component in your existing system that offers the least amount of performance. If, after you have experimented with different speaker placement, adding (or ridding yourself of) wall acoustic panels, carpeting, etc consider replacing and upgrading the least musical part of your system.
In Robert Harley's book "The Complete Guide To Home Audio, Sixth Edition" page sixteen's Upgrading a Single Component explains in detail how best to go about the process. Robert is also the Editor at The Absolute Sound magazine, he certainly knows a thing or two regarding building an enjoyable audio system and, his book has become a quality resource for the audio industry and audio hobbyists alike.
Here is a link to purchase Robert's book at Amazon (if you are unable to purchase from your local independent book store). https://www.amazon.com/Complete-Guide-High-End-Audio-dp-1736254502/dp/1736254502/ref=dp_ob_title_bk
*I make zero commission from this or any other recommendations that I may share.
Thanks very much for reading and subscribing to Hear More Music,
Doug