If you are asking if you can modify the pots themselves - no, you can't.
ask nigel said, you may be able to modify the circuit or just use a different value pot. If your pot is used for a voltage divider, it may well be ok but watch input impedence. For example as a simple voltage reference input to a comparator or opamp where the two sides of the pot are tied to the rails, twice or 1/2 the value will probably be fine.
In general, though, you really need to understand what the pot is used for in the circuit.