What Christopher said.

Other than reducing the saddle height by removing it and sanding down the saddle bottom edge on a flat sheet of glass which just isn't necessary of a new Yamaha FS800 to affect spec. action, the only end user adjustment for adjusting action is truss rod adjustment. It looks as if the tension of the new strings may be higher which has caused the neck to bow concave requiring a minor truss rod adjustment. Other than seasonal or location temperature and humity climate change requiring it, that's it.

I restring my own, often, own and play four different acoustics including two smaller bodied Yamaha acoustic instruments.

[br]For acoustic strings, having tried a few, I use and so can endorse & recommend with confidence D'Addario [u]uncoated phosper bronze[/u] for tone and feel. Not only is the price also right, but they are widely available. I choose to use EJ16s which are 12-53s aka Lights, which is the gauge which would have come supplied default on the FS800 but in EXPs. I find that gauge offers an excellent compromise of tone, feel and playability f[u]or me[/u]. You might prefer to try EJ15 10-47 Extra Lights, if you found the original strings of too high a fretting tension.

Either way, after fitting them, adjust the action to reference spec. by means of the truss rod, and lube the nut slots with a lead pencil. GL.