How to get Android L's performance boost right now

You don't need the newest version of Android to get all of the performance benefits. Here's how you can speed up your Android device in one easy step.

Google on Wednesday announced an update to the Android operating system at its I/O developer conference in San Francisco. The latest version, code-named Android L, includes a revamped notification system, an updated user interface, smarter unlock features, and a new battery-saving mode. The update, which will officially arrive on devices later this year, also promises to double app performance thanks to the new ART runtime. However, many people aren't aware you don't need Android L to enable ART on your device.
Google introduced ART in 2013 with the Nexus 5 and Android 4.4 KitKat, which means your device must be running KitKat for this process. Even so, however, not all Android 4.4 devices support ART at this time. I can confirm that this method works for the HTC One M8, Samsung Galaxy S5, Moto X, Moto G, the Nexus 5, and 2013 Nexus 7. Some other phones, such as the Korean model of the LG G2, also have the ability to enable ART.
Head over to the settings menu, select About Phone, and click on build number seven times. This will enable your device's Developer options, which will give you access to more advanced settings.

From the settings menu, select Developer options, scroll down to Select runtime, and choose ART. After rebooting, your device will begin to optimize your apps for the new runtime. This should take a few minutes, but when complete you will notice a considerable performance boost on most devices.
I should warn you, though, that some (and I mean very few) apps may be incompatible with the ART runtime. If one of the apps you use is unable to open or you are having trouble receiving a software update, simply switch back to Dalvik mode using the same process.