Difference Between 5K and 10K?

You will have to provide your schematic for any answer to that.

 

I can briefly cover 'typical uses' and see what applies.
The 3 terminals on a potentiometer are often either used as a variable voltage divider, or as a variable resistor.
A variable voltage divider puts pin 1 and pin 3 on VCC and GND, while the 'wiper' on pin 2 goes to a microcontroller or other voltage sensitive 'input'. The value of the potentiometer in this instance does not make much of a difference. A lower value may waste more power and too low can cause the potentiometer to fail.
Using it as a variable resistor requires a proper value to be selected. You 'Can' fudge the value though... if you design for a 10K but the desired result occurs when the potentiometer is set to less than 5K then you can use a 5K... you cannot use lower, and you can most certainly use higher. Using lower reduced the amount of adjustment you have, and using higher will make the adjustment feel clumsy and over-sensitive.

There are other cases of course, and we cant say exactly which until we see the circuit.

 

If you are only using 1 and 2, then it's not a divider... A divider uses 1 and 3 for power and ground, and pin2 can be adjusted to any voltage inbetween... you cannot do this with two pins.
In your application, you would be limiting yourself or operating our of spec.
I don't really have much else to say till I see a schematic though. I'm guessing based on details you are sharing, but there are lots of details that arent available.