You can change the inner ring to a 30 at the same time and run 30/46 which is what a lot of us old codgers do.
You will have to shorten the chain then or as Bernster says, you're probably best to fit a new chain anyway.
Measure the chain length by putting it over small front chainring and smallest rear sprocket, the derailleur will be folded over itself, have just enough chain length so the derailleur isn't touching the chain underneath it.