Once you have that, be prepared to a long process. Your ears were pierced at size 18g. The next size up will be 16g- this will be an easy stretch since it is so small. The sizes 14g and 12g are much the same- easy little stretches, with about a month of downtime to heal.
Now, 10g and beyond is a little harder, and will require longer waits. Wait two months when stretching from 12g to 10g and 10g to 8g. These will require a lubed taper, and might sting (but shouldn't hurt too bad, and should never bleed). 8g to 6g, 6g to 4g, and 4g to 2g, wait three months, and same deal with the taper. Then, 2g to 0g and 0g to 00g, wait four months. Anything bigger, you can wrap your jewelry in tape to gradually stretch, or wait even longer between stretches [even if you don't plan on going this big, I thought I would tell you]