Hello
Do i need to uninstall previous version of IDE and install 1.6.8 ?
Thx in advance
No idea; but is newer better for you situation?
I'm still recommending 1.6.5r5 until they release a version that doesn't introduce bugs that interfere with functionality for many users.
If you use the .zip installation package, you can install multiple versions.
However, Arduino 1.5.x leaves behind debris that interferes with 1.6.x versions, so those can't coexist. 1.5.x was always pretty rough though - it wasn't solid like 1.0.6 or 1.6.5r5 - so it's not the sort of thing you feel like you have to keep around.