Network Monitoring

I’ve just started at a new company and one of my jobs is to troubleshoot some network issues. The main issue is slowness of the network. I’ve started to uninstall unessaccary protocols on clients machines but we still run some old systems here whichare being phased out gradually. I’ve read somewhere (cant remember where!) that is is prudent to reboot hubs every week to relese unwanted packets. Also is there anywhere where i can find simple instructions on how to analyse a network?

Cheers