Clean install help

My laptop is going on 7 years now and it's starting to slow down a little bit. I wanted to do a clean install to get rid of some junk. The only problem is that it originally came with Windows Vista and I installed Windows 7. I purchased Windows 7 online so it is a file. The file is on my external hard drive. If I did a clean install, could I just install windows 7 again from my external hard drive?

Also, any suggestions on other ways to help clean my computer? I defrag weekly, clean up junk files daily and have done all of the optimizations that Brink has posted on Optimize Windows 7 (besides SSD).

linnemeyerhere said:

No you just need to back up everything of importance to a different hard drive and if there's room maybe do a image to the back hard drive as well. Then damn the torpedoes and begin the clean install:
Clean Install Windows 7[3]=Installation%20and%20Setup

Have all your drivers ready as well.

I have a copy of Microsoft Word 2007 from my buddy. Can I back that up or will I need to re-install that with the product key?

Everything you need is here to get a perfect Clean Reinstall - Factory OEM Windows 7
including the latest official installer and tool to burn to DVD or write to flash stick since you need a bootable installer and repair disk.

During install I'd delete all partitions to create new as you please per the tutorial.