Call the institution that you attended for schooling to acquire school records. All institutions have "Retention Guidelines for Schools," which contain specific protocol for the amount of time that school records must be kept. If the time frame specified in the retention guidelines exceeds 16 years, then the school should have the records on file. If not, then the institution will have to do some digging in older files to find the records. This might take some time.
Determine if the institution you attended uses a GPA scale. If the GPA scale is used, then it will be noted on the transcript as one of the final academic scores. If not, then there will not be a GPA score and it will need to be calculated.
Calculate the GPA if your school grades are available for conversion. An "A" letter grade converts to a four, a "B" is a three, a "C" is a two, a "D" is a one, and an "F" is a zero. A letter grade with a "+" has an addition of 0.3 and a letter grade with a "-" subtracts 0.3, which means a B+ and a B- is a 3.3 and 2.7 respectively. After you have converted all the grades to numerical form, an average of all scores will then give you the GPA.