2 seperate installation 1 theme same server

i got 2 separate installation on the same folder
each in their own sub folder – they use the same theme
which i copied twice.

Every time i edit a file i need to do it twice and its
a real hassle… How can i define so that they both
use the same theme – a shared theme but a different
database?

I have no “initial code” to share since i don’t know
where to begin so an example code would be much appreciated

Three fast and easy options™:

1. Setup revision control (git) for your theme and just pull/push the data around.
2. WordPress Network
3. Create a symlink to your theme folders

Option 1 is the best because it’s doesn’t matter which theme you edit.