The newest Apple flagship smartphone, iPhone 6, was recently released in September and in less than one week it has sold more than 10 million units. Now, users of the previous model, the iPhone 5s, are wondering if they should opt for the upgrade.

Checking out some of the specs of both devices should help users sitting on the fence about that decision.

In terms of dimensions, the iPhone 6 is 6.8mm thick and has a 4.7-inch screen size with 1334 x 750 display. On the other hand, iPhone 5s is thicker with 7.6mm width and has a 4-inch screen with 1136 x 640 IPS LCD display. Both have gold, light or dark silver available colors.

The iPhone 5s has an A7 chip processor, while the iPhone 6 has the latest 64-bit A8 chip which enables its CPU to perform 25 percent faster. There are also reports on a slight difference between battery life of the two smartphones.

The iPhone 5s has been found to last up to 9.4 days on standby with its 1,560 mAh battery. While its successor is powered by a larger 1,810 mAh battery and could last up to 10.4 days.

Comparing the smartphones in terms of storage options, the iPhone 6 has a variety of choices from the 16GB, 64GB and 128GB. For the iPhone 5s, since Apple has already stopped selling the 64GB version, customers can only obtain the 16GB and 32GB models. Of course, both the iPhone 6 and iPhone 5s do not support microSD cards.

Apple has also addressed the problems that come with taking photos with shaky hands via its new feature- digital image stabilization in their latest smartphone. Similarly, iPhone 6 stayed with 8MP rear camera specs like the IPhone 5s, but this time with 1/3.06-inch sensor, true tone flash, dual-LED flash and phase detection. The latter, meanwhile, has a slightly bigger aperture and camera sensor size.

With all mentioned differences and improvements, both smartphones still share similar features including Siri's voice control, built-in TouchID sensor, compatibility with the Apple watch and iOS 8 support.

Apple users, especially ones that have the iPhone 5s, are torn between going for the latest smartphone iPhone 6 or keeping their handy iPhone 5s for now. Given this information, the decision for upgrade will still depend on the customers' personal preferences and needs.