Sliding window protocol when number of packets is equivalent to the window size
Definitely, the window boundaries will be updated, in other words, the window will be shifted regardless of the fact remaining packets are strictly less than window size.

But the main point is after shifting,window will not be fully      occupied.The window in sliding window protocol is a buffer, which stores only those packets whose acknowledgement is not received. But because the packet 1's ack is received, it would no longer remain in the window.