Glyde.com offers some of the best trade-in value for older iPhones. (Glyde.com)

Apple has sent out invitations for a press event next week at which it will very likely announce new iPhones, so if you want to sell your old device, now is the time to do it.

The Cupertino tech giant will hold its event on Sept. 10, and some reports say the new iPhones could go on sale as early as Sept. 20. Apple is expected to announce the iPhone 5S, a successor to the iPhone 5, and the iPhone 5C, a low-cost version of the phone that is expected to have a plastic shell and come in numerous color options.

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This all means that if you want top dollar for your older Apple iPhone, you'll want to sell it as soon as possible because from here out, it will only keep losing value.

So where and how should you sell your device? Here are a few good options depending on what you're looking for.

If you want to go the safe route: Apple

If you don't want to worry about selling your device and you simply want to go with a brand you trust, then head to Apple's website and use their Reuse and Recycling program to trade in your old iPhone.

There, Apple will ask you a number of questions about your device, including what version it is, how much storage it has and the color of the gadget. You'll also have to detail how the device functions, how much damage it has, and whether or not you have all of the parts, such as the charger. Once you select which carrier your phone works with, the website will give you an estimate.

Right now, you can get $336 in Apple credit for an AT&T 16 GB iPhone 5.

If you choose to sell your phone, you'll receive a package so you can ship it, and later on, you will get a gift card that can be used at Apple's online and retail stores.

If you want the most money possible: Glyde.com

For top dollar, you'll want to go with Glyde.com. There, iPhone owners can list their device and get more cash back than they can from other websites.

Glyde.com will ask sellers whether everything still works properly on their device, how much damage it has, and whether or not they will include a charger. For a Verizon 16 GB iPhone 5, sellers can currently get as much as $364.68.

Once another user chooses to buy the device, Glyde.com will give the seller two days to ship the iPhone.

Glyde.com offers the most cash back, but if you choose to list with the website, make sure you understand there is no guarantee anyone will decide to buy your device.

If you want the most value possible: GameStop

Glyde.com offers the most cash, but you can get more value by way of store credit if you trade in at GameStop.

According to its online trade-in calculator, GameStop will offer sellers $400 of in-store credit for AT&T and Verizon versions of the 16 GB iPhone 5. To get that price, the device must be like new -- meaning everything works and the device looks as thought it is "right out of the box" -- and come with its charger.

Sellers must use GameStop's trade-in calculator to get and print their quote. After that, they must take the quote and the device to one of GameStop's retail stores in order to get their store credit.

If you're a gamer, this is a trade-in option worth considering.