how can i fix a 2002 slimline caroma toilet that keeps overfilling? ?

if the float and arm inlet system at the water inlet end of the arm should be a plastic threaded pin with a plastic nut on it. Release the nut and turn the threaded pin in closer to the inlet valve pin so when it fills it will shut off earlier so not reach the overflow. You then re-tighten the lock nut. Re-adjust if shutting off and not letting in enough to flush.
Any other type don't know.

BB
May 2011