Can I change judges?
It's called recusing a judge.
Judge shopping is not permitted.
In criminal courts judges are assigned to cases randomly. You cannot choose a judge: you can only ask a judge to step down.
The standard is whether the facts would place a reasonably prudent person in fear of not receiving a fair and impartial trial. It is a question of perception; it's not a question of fact.
Judges can be disqualified for communicating with either party privately, showing bias, prejudging someone, not appearing impartial, taking sides, helping either the defendant or the prosecutor by giving them tips or advice in court, or having the appearance of favoring one side over the other.