It's pretty easy. The first is to take the whole test again, ironically very few opt for that one..
Basic: Approved refresher, 48 approved CEU's, renewed CPR and verification from EMS Supervisor.
Advanced and Paramedic: Renewed your CPR, (and ACLS if Paramedic or I/99). Then complete the mandatory refresher (according to your level, how long that would be) and then complete the required number of CEU's per level. Basic 48, Intermediate 36, and Paramedic 24. Remember the shorter the CEU's the longer the refresher, so everyone is about the same in re-certifying. Another option for Paramedic is to take AMLS, ACLS, PALS, PHTLS in lieu of refresher, be reminded you will still need additional CEU's (one cannot count those classes as CEU's, if you are using that option)
If you are an advanced level, then one must have your medical control or approved licensed physician to sign either they witnessed you perform your skills or perform them in a lab setting..(i.e classroom)
Be sure to have all CEU's verified by training officer, and Supervisor sign that you are currently working or acting at that level, as well as the medical director.
Send your money order to NREMT.
Now, always make extra copies for back up. As well some states have an agreement that NREMT re-registration requirements are similar or supersede them, so a letter from the State maybe all that you will need.
** If recertifying for State & using same material, be sure your state uses the NREMT method.
Be sure all material is before March of your expiration year. Now is the time to be near completion.