Server Uprade Issues

[eluser]Unknown[/eluser]
I am using Codeigniter version 2.0.2 for my application.

For security and performance reasons I want to upgrade PHP, MySQL and Apache on my server.
Once the upgrade is complete the server will be running the following latest versions:
PHP 5.3.16
MySQL 5.5.25-1

I'd like to know, if I will face any problems with my application because of this upgrade.
Also if any one could guide me on what necessary changes I may have to do.