How to change chainrings on this Tiagra crankset? I want to switch to 46/30 but don't know how to begin. The crankset is Shimano Tiagra FC-4700, 50x34T, 170mm
The crankset (110 BCD - Bolt Circle Diameter) is unlikely to accept a 30T chainring. It definitely isn't supported by Shimano. You need a new crank.
Look at subcompact cranksets like, e.g., FSA Tempo Adventure (10/11 speed). Note that this specific one also uses a different bottom bracket.