Replacing toshiba hard drive

I need to know the best hard drive to purchase for my Toshiba L305-S5921 with Windows Vista home premium. The current drive readable and the tech said with a brand new hard drive it will run just like new. I don't know where to start, but I want the best one that will run excellent. Another question, what does the hard drive contain and process, and how much can I upgrade windows using a new hard drive? What other hardware would stop the compatibility of my laptop upgrading software? Will add info if you ask questions
 
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