Check in task manager to see which processes or applications are taking up the most cpu and memory.
Scan for virus and malware
Get rid of all those toolbars and addons for your browsers
How much disk space is left you need at least 20% the size of your drive.
Use CCleaner to get rid of a) temporary files b)safely clean the registry c) stop necessary programs from running at start up
Surface Pro 5 News - release date, UK price, features, specs