Probably the biggest reason to root and install custom ROM is the fact that you can update your phone with updated software from a newer phone. In this case, you can in fact turn your Galaxy S5 into Galaxy S6 by using a custom ROM like Sixperience ROM.
The Sixperience ROM has been ported straight from a real Galaxy S6, giving you all the new software features including Galaxy S6 theme engine, resizable floating windows, S6 apps, and much more. Of course, you get a nice AROMA graphical installer also, allowing you to choose from three different kernels (you can overclock using Boeffla or KToonsez kernel) and even choose from two cameras (Note 4 or S5).
This ROM can be installed on most S6 models including SM-G900F/G900I/G900M, Canadian SM-G900W8, T-Mobile SM-G900T, Korean SM-G900S/K/T, and few more. (AT&T SM-G900A should be supported soon.)
There are couple things not working like fingerprint sensor (as S6 fingerprint software is not compatible with S5 fingerprint sensor) and world clock widget but other than that, the ROM itself runs rather good with great battery life. If you are looking to turn your Galaxy S5 into an S6, definitely try out this ROM this week(end) and do let me know what you think!
To install, reboot into recovery, make backup ROM, wipe data/factory reset, install ROM, install Gapps, install SuperSU and reboot. (If for some reason you end up in a bootloop or get force-closed keyboard error on boot, reboot into CWM recovery, go to Mounts & Storage->format /system. For TWRP, go to Wipe->Advanced Wipe->Wipe /system.)
First time installing a custom ROM? See How to Install Custom ROM on Galaxy S5! Using TWRP? See our universal fail-proof method on installing custom ROM and boot the first time!
Want Flash Player? See How to Install Flash Player on Android Lollipop!
If you want some awesome audio, check out Viper4Audio FX MOD, which you can install on this ROM to enhance your music 100%.
If you want to run your apps in tablet/hybrid/custom DPI mode, see our Xposed App Settings guide.
Need to run apps that check for root? Check out How to Run Apps that’s don’t run on rooted Android!