You can simply just do this:
$epl['Chelsea']['pts'] += 3;
This will add 3 to the existing value and store it in the same place. This is the equivalent of writing this line:
$epl['Chelsea']['pts'] = $epl['Chelsea']['pts'] + 3;
The +=
and -=
operators both work in-place, so += will add the value to the right to the variable on the left and store it in the variable on the left, and -= will subtract the value on the right from the variable on the left and store it in the variable on the left.