Assuming that you have a table with a member's id column that also contains the "number of games played" (or perhaps it's in the SMF members table), load all the members from that table into an array. i.e. $mymembers[ ]. Enter a for loop $x, $x < count($mymembers[ ]), $x++ and update each record in the SMF members table SET money=money+(your forumla for counting the increase) WHERE `ID_MEMBER` = $mymember[$x][member's id] etc.
You can add a link to the function in the menu of the Admin Manage Members section and just click it to do the deed.
If you're unable to write the code, if you'll post all the pert. db info up, as soon as I have the chance I'll do my best to write it up for you.
Phydeaux