Test the voice before the shapes
Find the highest sustained phrase and the lowest important phrase in the song. Sing them gently in the current key and notice where the sound becomes strained or unclear. A key that starts comfortably can still fail in the chorus. Avoid choosing a new key solely because it replaces one difficult ukulele chord with an easy open shape. Your accompaniment serves the complete vocal line, so the workable range needs to be established before finger convenience becomes the deciding factor.
Move the entire progression consistently
Use transposition in AudioChords as a chart aid and verify each new chord on the instrument. Moving a progression means shifting every root by the same interval while preserving chord quality and any specified bass relationship. Do not change only the awkward chord unless you are intentionally reharmonizing the song. Check whether the audio reference you use is still at its original pitch before playing along. A transposed list of symbols and an unchanged recording will not match merely because both show the same section of the song.
Check the hidden difficulties
Play the verse, chorus, bridge, and ending in the proposed key. A new key may simplify the main loop while making a short turnaround harder. Compare the strumming feel and the register of any melodic figure you want to keep. Write down the sounding key and tell other musicians before rehearsing together. If two keys both suit the singer, choose the one that offers more reliable transitions and a pleasing instrument sound. Transposition is a practical arranging tool, not a requirement to make every song use the same small collection of familiar ukulele grips.