To assign a static IP you need to edit /etc/network/interfaces.

The interface will probably be called eth0.

The current entry will look something like

auto eth0
iface eth0 inet dhcp
You will need you need to change this to:

auto eth0
iface eth0 inet static
   address 10.253.0.50
   netmask 255.255.255.0
   network 10.253.0.0
   gateway 10.253.0.1
   dns-nameservers 8.8.8.8
You will have to change the numbers around depending on you network, but you can find out the information by checking out ipconfig from Windows.

Make sure you choose an address outside the address space of the dhcp server

Then restart networking sudo service networking restart. If that gives you trouble reboot the machine.