In reply to irshad_mansur123:
You have a packed struct with 26 integer. So the total size of the packed vector is 26*32 bits.
These are packed from a to z where the 32 bits of a are in the MSB and the 32 bit of z are in the LSB position.
If you want to change the value of member y to 22 , try a2z_struct[63:32] = 22;