Middle Earth map improvement ?

[vantech]

Hi, i'm trying to print a poster of this Middle Earth map :



I tried to find a better version online but this is the best one i found.
What can i do in Photoshop in order to improve the quality of the print ?
I changed the dpi to 300 and i would like to sharpen the image if possible since the poster will be 160cm / 91cm

Any help would be greatly appreciated !

 

[dv8_fx]

Hi there.... What version of Photoshop do you use?

 

[vantech]

Version 13.0

 

[Zeealex]

That's CS6, right? just to confirm this.

 

[vantech]

Yes CS6 V13.0