Exit the command center. You can eliminate the two soldiers in the center of the location by firing a poison arrow. There are still two more left behind the truck, at the main gate. You can easily get them from behind and choke them.
As soon as you eliminate all of them, cross the gate close to Lenin's statue. Stand next to the stump covered with rope and aim at the horizontal beam covered with rope. Lara shoots an arrow that extends the rope. Over the rope, get onto the fragment of the destroyed stairs below.
Jump off the stairs towards the windows and walk around the building. As soon as you get around the corner, climb into the room, through the opened window.