You can now slide the upper receiver forward. It may take some pulling to get it to move.

Attention: Although it is easier to pull the receiver off with the dust cover in the open position, avoid the dust cover colliding with the extended body pin as shown by the square marker. The open dust cover will prevent you from moving the receiver forward and could potentially bend the body pins with excessive force.

After this step, the spring and charging handle might fall off, which is okay.