If I reformat my computer

I have a laptop that is a few years old but I really like it and want to keep it. It has gotten sluggish and I dread the idea of reformatting, which i've never done to any computer. i run the disk cleanup, defrag, and registry cleaner often but it's still slow.

 

So my question is about my NIS. I have several months left on my subscription. My account info says I have no more downloads.  But if I reformat the computer, can I download NIS again (reinstall) onto the same computer?

 

And I guess I'm hoping someone might have another suggestion for regaining some speed without reformatting.