I tried to install gnome-tweak tool but its says
The following packages have unmet dependencies:
gnome-tweak-tool: Depends: python (< 2.8) but 2.7.3-0ubuntu2 is to be installed
what should i do to install gnome-tweak tool ?
You will have to install the depending python version from Synaptic Package manager.Gnome Tweaks depends on that, as your message clarifies.