Raghav - please always include a link to the datasheet so that we^[1] can see what it actually says! Meanwhile, lets look at the table that Charles helpfully posted:

What is that telling us^[2]?

The left-hand columns show the high-order data bits D5, D4;
The rows along the bottom show the low-order data bits, D3-D0;
Each cell in the table represents the character displayed in response to the 6 bits formed from its row & column number.

Thus:

Binary    Hex  Char  ASCII: Hex Binary
00 0000 = 00 = '@'          40  100 0000
00 0001 = 01 = 'A'          41  100 0001
  :
00 1111 = 0F = 'O'          4F  100 1111
01 0000 = 10 = 'P'          50  101 0000
  :
01 1111 = 1F = '_'          5F  101 1111
10 0000 = 20 = ' '          20  010 0000
  : 
10 1111 = 2F = '/'          2F  010 1111
11 0000 = 30 = '0'          30  011 0000 
  :
11 1001 = 39 = '9'          39  011 1001
  :
11 1111 = 3F = '?'          3F  011 1111

Thus it is just using the bottom 6 bits of the ASCII code - so no need for any conversion at all!

[1] "We" = more than 1 person, where one of them is me.

[2] "Us" = the general readership of the document, assumed to be more than just me.