Start with a wired baseline
Plug a laptop into the router with Ethernet and run a test. That number is what your line delivers before WiFi enters the picture.
If the wired result already misses your plan, the issue is upstream and worth raising with your provider.
Fix your channel and band
2.4 GHz travels further but is crowded. 5 GHz is faster and cleaner across shorter distances.
Set a fixed, low-congestion channel rather than leaving the router on automatic.
Placement beats hardware
Central, elevated and away from metal, mirrors and microwaves. Moving a router two metres often outperforms buying a new one.