Search at Youtube just for iPhone 4 replace battery, there are many useful video tutorials. The change is minute with some caution and judicious approach in 15. done.
Battery and one cross and Pentalobe Screwdriver are neatly packed in small carton and plastic bag.
After the change and subsequent charging, I was very pleasantly surprised. The iPhone has almost exactly the battery life that it had beginning with the original battery. If the battery is now also holds a few more years, all is well.
The quality of the tool is not particularly good, but you can easily make the switch so.
I'm very satisfied.