Hi @__tkeyah,
Welcome to the Bunnings Workshop community and thank you for your question.
Yes, it is possible to remove bricks, but if you are removing too many without reinforcing the structure in some way, such as adding a lintel above the parcel box, you risk things falling down. This is not the end of the world, as you could always rebuild using the same bricks with some new mortar, I just think it is important to mention.
If the parcel box is fairly strong, it will also add to the support once installed.
To remove the bricks, you would need to cut them out using a demolition saw or a large angle grinder with a masonry cutting disc.
Once the cuts have been made, you can use a club hammer and brick bolster to help remove them.
Check out How To Cut a Brick Wall Opening and How To Install a Lintel for some examples of similar projects.
Let me know if you have any further questions.
Jacob
