app update wont install

[briandress]

so i downloaded the build that is posted with today's date and attempted to install it via sideload on my Nexus 5...I accept at the prompt screen and it goes into the instal screen but i get an error saying that the application is already installed with a conflicting signature...can anyone shed some light on this? also...is there a way to back up my save data so that if i have to uninstall and rteinstall with the new build I will not lose my save data? thanks in advance for all the help...please feel free to tear me a new one if i have put this question in the wrong place. I looked but couldnt find an answer...