Take the ring to a professional jeweler
Determine whether the ring needs to be made larger or smaller
Have the jeweler measure the correct ring size
Choose the resizing method based on the ring design and metal
For a larger size, add metal to the band
For a smaller size, remove a section of the band
Rejoin and solder the ring
Clean and polish the ring
Check the fit after resizing
Avoid resizing rings with certain stones or intricate settings without expert advice