How to publish & back-up to local computer

I am wondering how to make edits to website on local computer rather than through dashboard (ex: site.com/wp-admin). I am new to WP and have created site through dashboard using a template that was purchased, but having lots of issues with the site being slow as well as moving within dashboard (to make edits/additions) being very slow . Was told by host (ReadyHosting) that we should be on Linux server rather than on Microsoft server, but was also told that working on the site on computer rather than online (through dashboard) would resolve some slowness issues. Suggestions?