They pull straight up, each button has a slot for the tongue on the button, it’s a friction fit
If it looks like some buttons are more proud or recessed than others it’s because they’ve been pressed into the slot less or more
When putting the replacement on, just do it gently until it aligns with tops of others
My A4 had buttons all over the place (from new) and I used to think the PCB was sinking, it was just that buttons had been pressed in too far during assembly
Hopefully Elektron will guide you through it, but gentle pressure from a pair of pliers covered in insulating tape will prise it up no probs if you pull straight up, then to replace press down using your finger