Everywhere I look, it says something like "the embouchure needs to be modified" but never says how. so is there anyone who might be able to help?
It's pretty difficult and takes a long time to get good at. The term that's usually used to describe the technique is voicing, which means shaping the mouth and throat, and positioning the tongue, in order to make the high overtones sound out. And it's really hard to teach because all of that is inside your head and a teacher can't look at it to see what you're doing. A very good in-person teacher can listen for common signs that you're doing things right or wrong, but it's going to be impossible for anyone to give specific advice to you through a channel like this.
One exercise to get you started: Play a second-octave note, for example 4th line D. Sustain it for a bit, then let go of the octave key and try to keep the note from falling down the octave. Don't use your lips or jaw to do this (biting the reed), use your airstream. Then, take the horn off your face, reset, and try to come in on that note.
In general, if you can get pretty comfortable playing overtones of first-octave notes, you'll be on your way.
This may or may not sound weird, but focus on shaping your inner mouth differently.(Throat, tongue, jaw) I find the raising the back of my tongue the best way to start experimenting with altissimo. The best thing is to just experiment with shaping your mouth in different(and/or uncomfortable/unnatural) ways.
Try to open your throat as if you are saying "ee". The jaw needs to drop down a bit in the embouchure. Also, different fingerings work for different saxophones, so experiment to see which ones fit for yours.