I want to get rid of this ugly brick grille in front of the window.
Which ugly brick grille do you mean? - I see
two grilles there: an ugly one and one made of bricks. I would remove the ugly one, and that should be relatively easy: judging by the picture, it seems likely that it is only mortared into the bed joints at four points. Once that's gone, the remaining brick-hole matrix makes an aesthetic impression. If you wanted to remove both, it would be considerably more complicated: you would not only have to saw through six bricks on each side and chisel out the joints in the bottom row, but the lintel would also be missing (at the comparison window you can see a brick roll layer at the top). The question would also be, what is the point of the whole thing - because: would I be a rogue if I suspected this to be the window of a guest WC at this point?