You could use a template letter such as this one. Make the appropriate changes, so it would fit your needs and add some addtiional informations :)
Name of your school
Hello! I am writing this letter to give you some feedback about our science laboratories. The world is going forward at an extreme pace and I think that we need to upgrade and innovate some of our equipment. Unfortunately, some of our materials there are already obsolete and inaccurate and it may affect some of our experiment during class.
I hope that you grant this request for the sake of the students. Thank you.