What I should do when overheat

A few questions first:

- Did you drop your phone and this started happening?

- Where exactly is the front display separating at? I assume it's the glass separating from the plastic frame. Has the screen been replaced before?

It sounds like your battery has gone bad and has expanded. You will probably need to replace the battery.

You can get the part from here:

iPhone 5 Battery

Repair guide:

Reemplazo de la batería del iPhone 5

My replacement guide instructions:

It is fairly simple. Basically taking two pentalobe screws from the bottom of the phone out. Then pry the screen up from the bottom then work your way up. Do not take the screen out as it's held by front display cables at the top of the front display and you should lift up the screen to like 45° a bit more is okay too then unscrew the two screws near the battery connector. Don't mix these two screws up for convenience and then unplug the battery connector and then lift up the battery from the left side with some prying tool then put the new battery in. You may need some new battery adhesive if the battery won't stick on.

Color going yellow / discolored when putting pressure on the screen is a good indicator that the battery may have expanded and is pushing against the screen under it.