Preview not doing what it should?!?!?!

[muvuth]

I'M SO FRUSTRATED I NEED ALL CAPS FOR A SEC!!!!!

OK.

So.
I'm trying to save some files in a smaller size, pixel-wise.
I've always worked with bytes when downsizing so this is new to me. I try to change a file called "Original file", which is a 4.1 MB file of ab. 600x4500 pixels, want to make it 3500xwhatever.
So I open Tools > Adjust size, I change the size, and it tells me it'll be 1.4 MB, which is pretty much what I need.
I change it and save it with a new name, "Mac sucks now" followed by a random series of digits just to show you I'm not making this up.
Then, when I check the resulting file, and when I check... IT'S STILL 4.1 MB!!!!!!

I mean, how am I supposed to work with this s*it Apple is making in the last years?!?!?!?!?!

I really need some help here, either a Mac expert or a frickin' therapist to stop me from hammering this machine!

Kidding. But it's truly frustrating, working with a Mac is a nightmare since I upgraded from Snow Leopard (Mojave now).

Thanks to anyone who'll be willing to show me how to obtain what I'm trying to achieve

 

[BrianBaughn]

It's not much help, the estimated size thing.

If I open an image and go to Tools>Adjust Size… I first get this:

Which, without doing anything, in a few seconds changes to this:

 

[muvuth]

I see, thanks for sharing. I thought my Mac was hating me back, but I guess it's just another example of Apple using too much money on iOS dev and leaving Mac problems unsolved.

Good day buddy