Amateur Radio License are good for 10 Years with a two year renewal grace period.  So starting at 90 days before the expiration date you may renew your license before it's usefulness expires. Then from the expiration date you can still renew your license within two years, but after that your license is dead and you will have to take your test(s) again and file for a new license(s).

 
Renewing your license is easy  -  Don't pay anyone to do it for you,
bad enough you probably have to pay the new $35 FCC Fee.

(Note) I haven't renewed a license in a long time, not sure about the
accuracy of this, but bet the fundamentals of renewing are the same.

Renew your Amateur Radio License at  http://wireless.fcc.gov/uls  Read "New Users -Learn More".  As it states if you haven't done it or it's your first renewal, you will need to register thru CORES and get a password, after this is accomplished you will need to log-in to the ULS and enter your FRN (10 digit # on your ham license) and your password.  If your license isn't visible - then you need to associate your amateur license with your FRN # so your license will show up, and then you can begin the renewal process.  Click your licensee name-address box then continue, check appropriate boxes, verify all name & address information, recheck info & continue, type your name as on your license (title probably not necessary) and submit.  Print your confirmation page with your File Number or save as .mht type webpage.