I have a complaint about what you call a grammatical sentence!

Please email us the sentences you have had trouble with at info@playmationstudios.com and we will look into it.

I am having trouble signing into Game Center

Check out this help page from Apple.

How do I update my Game Center profile?

Enter the Game Center App from your homescreen. From there you can do things like add a profile photo and invite people to be your friends in Game Center.