'99 Escort heating problems.....

[cerati.z]

Hi guys, a couple of weeks ago i noticed the temp. gauge would shoot straight to HOT, but the car was not over heating, i was going to change the thermostat my self....is this hard thing....i have no mechanical experiance other than brakes & oil changes...someone told me that the ignition core? is in the way any help would be grreatly appriciated.....