We support php 5.6, 5.5, and 5.4 on all of our servers. If you want to continue using your older code you can, just change the php version.
If you want to update your code to run on newer versions of php I recommend making just a few changes at a time, and then put an exit; command and do lots of echos and var_dumps along the way to make sure everything is working the way you want. Then if that section is working move your exit; down a bit and do it again.