Here are some steps to remove the system install notification if you don't intend to apply the new update.
1. choose install later option select anytime like 1am
2. download Root Browser from Play store
3. open the root browser app and go to /system/app
4. locate SDM.apk app and longpress it to rename to SDM.apk.bak
This will temporarily disable those annoying system notifications until you decide whether you want to take the update.