After years of using the phone, I passed it off to my wife who used it infrequently. Unfortunately, more often than not the battery would be very low or completely drained when she went to make a call. When the phone had an issue charging, that was the final straw so we decided to replace the battery.
It took about 15 minutes to replace the battery and some of that time was dealing with trying to get the suction cup to hold on strongly enough to lift the screen off. Otherwise things went smoothly although my largish fingers did have a little trouble getting the one ribbon cable reinserted.
You can do it! Just read the instructions and you'll be able to get this replacement done without issue.