since upgrading to Lolipop...problems

[AC Question]

my S4 is doing all sorts of odd things. The numbers/letters of the lock screen start to blank out after afew days ( restored by re-starting) internet and apps work slower and battery life is reduced. Any ideas on fixing, text also locks while typing or is very slow, kit kat was fine..old saying 'if its not broke why fix it' grrr help!