If you have a packet like this : 
04 BB 04 00 00 00 06 00 08
and you want increase or decrease for example the byte in position 7 (byte = 06) by one each time a packet is sent:
-right mouse button on a packet logged,SEND
-double click or press INSER on the byte at the position 7(it will be show in red) and press play as usually
-wpe will send packet : 
04 BB 04 00 00 00 07 00 08
04 BB 04 00 00 00 08 00 08
04 BB 04 00 00 00 09 00 08
etc...
for decrease set the step at -1