The main circuit breaker on the side, at the outside out my house is
overheating and trips. All electricity inside the house gets turned
off when this hapens. It tends to happen whenever I use the AC on a
hot day. The electrician says that this 90 AMP main circuit breaker
needs to be replaced. The problem is that he says that they don't
make these 90 AMP circuit breakers anymore. They only have them in
100 AMP. He says it's safe to go up from 90 to 100 AMP.

Is this safe to do at my house? Your suggestions/advice would be
greatly appreciated.