Dont worry you can change your grades into percentage by following formula.

TGP*1.11 OR TGP*90/100

Where tgp is total grade points you can calculate from information below

Grades.       Points

A+.                9

A.                  8

B+.                7

B.                  6

C+.                5

C.                  4

D+.               3

D.                 2

E.                  1

Add the points you obtained in all subjects you get total grade points and apply the formula of converting grade into percentage mentioned above.