How to restore my MacBookPro 6,2 I would like to restore my 9 year old MacBookPro6,2 to its former glory. And to get rid of anything that might be slowing it down.
I have original discs. Do I have to go down that path to original OS or is there a way to restore it to some  intermediary OS online?

Once I do that can I update it straight to High Sierra (highest OS that my configuration supports) or do I have to go through all the updates one by one?
What state is it in now? If you can access the Mac App Store, then you should be able to install High Sierra directly from there.

If you can boot to a Recovery Partition (Command R on boot), then you can erase the hard drive and do a 'clean' install of the current OS, if that is what you want to do, and then update to High Sierra from the App Store.

It's unlikely that age or software is 'slowing it down'. A full, or failing, mechanical hard drive might do that. 

The best way to keep it useful is to replace the Hard drive with an SSD, and max out the RAM.