Okay, I have spent hours searching for a good, quick, easy, direct solution, which I think should do it hear. If you change your gmail password online from a computer; you then need to update your ANDROID phone gmail acct. password too, but in both places, there are 2, INCOMING AND OUTGOING, THEY are separate.
BEGIN AT HOME SCREEN,
GOTO APPS==>>> EMAIL/GMAIL APP
OPEN MENU (TOUCH BOTTOM LEFT BUTTON of phone open account settings (in the more string))
scroll down until you see SERVER SETTINGS; open BOTH INCOMING AND OUT GOING( HERE YOU FINALLY CHANGE YOUR PASSWORD) I never remember this stuff until I actually need it so I send myself an email online with these instructions in subject type password change, then whenever search you inbox for password references, I'm a stroke survivor and little things like this help us a lot. hope thats easier and that it all makes sense and helps. good luck.