Resizing is not the same process for every ring. A plain metal band may be simpler to adjust than a ring with stones around the full circumference, intricate engraving, or an unusual construction. Some materials and designs are difficult or impossible to resize without changing their appearance. Before making a decision, ask a qualified jeweler to examine the ring itself.
Explain how the ring fits and when it feels tight or loose. Finger size can vary with temperature and activity, so a jeweler may suggest checking the fit more than once. The goal is a ring that passes the knuckle comfortably and stays secure at the base of the finger. If the size difference is small, other options may be worth discussing, but temporary fit aids are not right for every design.
Ask how an adjustment could affect the finish, setting, engraving, or any maker's warranty. After resizing, inspect the ring and have the setting checked before returning to regular wear. Avoid trying to bend or alter a ring at home; doing so can weaken the band or loosen stones. A professional assessment is the safest way to understand the options for a meaningful piece.