1. Open the report in Crystal Reports
  2. Create a new formula and manually enter the numeric ranges for each letter grade:
    For example:
    if isNumeric({StsGrdsGrds_1_Grade}) then
         (if toNumber({StsGrdsGrds_1_Grade}) in 95 to 100 then "A+" else
         if toNumber({StsGrdsGrds_1_Grade}) in 90 to 94 then "A" else
         if toNumber({StsGrdsGrds_1_Grade}) in 85 to 89 then "B+" else
         if toNumber({StsGrdsGrds_1_Grade}) in 80 to 84 then "B" else
         if toNumber({StsGrdsGrds_1_Grade}) in 75 to 79 then "C+" else
         if toNumber({StsGrdsGrds_1_Grade}) in 70 to 74 then "C" else
         if toNumber({StsGrdsGrds_1_Grade}) in 65 to 69 then "D" else
         if toNumber({StsGrdsGrds_1_Grade}) < 65 then "F")
    else {StsGrdsGrds_1_Grade}
  3. Click Save and Close
  4. Insert the formula into the report