To achieve a comfortable and secure fit, one of several options for reducing or increasing the size of your ring, or to keep it from spinning, may be appropriate.
Sizing beads - Since your knuckles may be wider than your finger where your ring will sit, it's not uncommon for rings to feel slightly large when you're wearing them. To remedy this, sizing beads may be soldered inside the shank of your ring to secure your ring and keep it upright on your finger. Spring inserts or foldover devices are other sizing options to ensure a proper fit and upright positioning of rings.
Sizing up - If you need to increase the size of your ring, your jeweler can cut the shank and add a bridge, soldering the extra metal to the existing ring. Some rings may also be stretched without the addition of extra metal, though not all rings are candidates for this approach as the durability and appearance may be impacted. Only your jeweler can help you decide which method is best for your piece.
Sizing down - Similar to sizing up your ring, a ring may be sized down by cutting the shank and soldering together the ends. If your ring is an eternity band, you may have been told that it can't be resized. This isn't true: while resizing of eternity bands may require adjustments or replacement of some stones, and will include more steps than resizing a plain metal band, an experienced and trained jeweler can resize your eternity band. If your jeweler does not have the experience to feel comfortable doing so, ask if they can refer you to someone who may.
Other Jewelry Resizing
Resizing services aren't limited to solely rings. You may have bracelets , necklaces, or watches that need to be modified for either comfort or style. Many jewelers offer resizing services for free within a specified time frame after purchases you make at their store and may offer quick resizing on items like linked watches for a small fee if you purchased the item elsewhere.
Learn more about jewelry resizing here: Guide to Jewelry Resizing