modified ALL list item on flex grid using pushbutton command.

how can i modify all the rows on flexgrid using some command button, beacuse all i can do just stuck on the first row of flexgrid itself.

so lets say i hav 3items appears on FG, then with my pushbutton i want to modify the detils inside the FG.

name|absent|present|
---------------------
ariyu| 5 | 3 |
kent| 6 | 4 |
shinz| 7 | 8 |

so i want to modify the number using 2 command button, to increase & decrease.
but now what i face just stuck on first row, it wont move to next row.

all suggestion are highly appreciated.