Wrote an entire phrase in double time-is there a batch fix?

Sorry if this has been addressed in the forum or handbook - I wasn't sure of even the musical terminology to use as a search term that would address the particular "oops" I have made when notating my song.

I wrote a phrase with 16th notes and 8th notes - where really, 8th notes and quarter notes are what are called for. (darn it!)

I know how to change individual note duration, and I could halve each note individually, cut and paste them note by note, or I could simply reenter these 4-8 bars manually. But I wondered if similar to the "Q" shortcut which halves the duration of a single note, there was a measure or multi-measure level operation I could take on an entire phrase?

Thanks!