Ion Petroianu, VA3NOI
The small pot is for volume and it is the one that has the power switch on it.
If that is the one you want to replace buy a logarithmic pot not a linear one. It should be 10K as per LM386 data sheet..
For easier tuning you can use a multi turn linear pot.
You can use anything between 5K and 50K. It will not give you a better resolution (same 100 Hz step) but it will not be so sensitive to touch.