As part of Delta’s “streamlining” of the SkyMiles program, we are serving you all a final warning that on Dec. 31, all of the old Frequent Flyer Miles (those miles earned before the program changed to SkyMiles in 1995) will be converted into the newer SkyMiles.

This is a very big deal if you were a Medallion-level member in the old program. That’s because you can redeem miles at the reduced award levels once afforded to Medallion members. You can redeem just 20,000 miles (vs. the current 25,000 miles) for a free domestic roundtrip (including Mexico, the Caribbean, and Alaska) or just 25,000 miles for a domestic first class ticket. (When calling Delta to redeem your “old” miles, it is a good idea to tell the agent to use your Frequent Flyer miles because the system is set up to deduct the newer SkyMiles first.) Remember, these old Frequent Flyer miles need to be redeemed before years’ end.

And for all SkyMiles members, effective Dec. 31, miles will expire after two years instead of three — another sign of Delta’s “streamlining.” Any member who has not had activity in their Delta account within the calendar years of 2005 and 2006 will see their miles disappear at years’ end. This includes any old Frequent Flyer miles that currently don’t have an expiration date — these miles will be converted to SkyMiles as of Dec. 31 and will be subject to expiration.

If you’re not sure of the last time you flew Delta, this is the time to earn those miles to keep your account active. Any activity in your account will extend the expiration date. An easy way to save your miles is to go to https://www.delta.com/marketing/insideropinion/index.jsp and take the Insider survey to earn 250 miles. Alternatively, register your credit cards with the Delta SkyMiles Clothing Care program. Register online at skymilesclothingcare.com to earn one mile for every dollar spent at participating dry cleaners. Do it today. Miles for these offers take six to eight weeks to post to your account.