streamline Wordpress php to solve high cpu usage and downtime problem

We are currently running a Worpress application on a dedicated gatorhost server. We are experiencing constant downtime when the page gets a lot of traffic. We have approx. 1500gb of bandwidth a month. Apparently there are php calls that remain on the server as defunt php. My goal is to streamline wordpress to the bare essentials considering the page we are running right now. First step is an audit of the php calls that are overloading the server. Second, Eliminate php calls that are not being used and overload de dtabase, eliminate all that is not necessary on the wordpress installation. Clean the mysql server.