Phone's performance is directly influenced by the running applications and services and its memory. Try removing all the applications you don't need or install only one app which covers the functionality of 3-4 apps. You need to clean the cache files as well. You can do this with a cleaning application. Cache Cleaner+ is more than enough to clean the necessary files. If you don't care about the installed applications and your stored data, you can perform a factory reset operation to set the phone to its factory defaults (great performance increase).