This is not made out of solid wood, and, in particular, the top and bottom pieces may be low quality chipboard with higher quality sections near the edges where the mounting hardware is to be installed.
So this might not be possible at all, and it will look rather weird, as it won't be a 3x4, but something closer to a 2.5 x4
But if you really want to do it, cut 57 cm off of the top and bottom pieces. Best tool for this would be a table saw, but you can accomplish this with a hand saw or a circular saw if you are very careful. The cuts have to be parallel and square
After that, you'll need to move the mounting hardware from the cut off piece into the new cut off piece. You'll probably need a drill for this. Then you'll reassemble the frame. Now cut the square blue pieces down to size.
If done correctly, you won't need to paint anything.
But probably easier to go to your local second-hand furniture shop and find something that fits better.