I used my Pro tech Toolkit to replace the Battery in an old IPhone 3Gs phone so that My grand son could have it to play games on and watch videos.
I was nervous to start and was frustrated on more then one occasion. But I worked it out and when all was done, It was a success.
Take your time and go step by step. Walk a way for a second and clear your had and cool off if things go wrong. Hurrying and trying to work when upset will only cause more problems. You can do this. You have the tools and ifixit has the knowledge.