Can I Change the Number of Shards to Four with Two Replicas When There Is One Shard Set in the JSON File?

Once an index is created, the number of primary shards cannot be changed.

You can run the following command in Kibana to change the number of replicas:

PUT /indexname/_settings
{
"number_of_replicas":1       //Number of replicas
}

index specifies the index name. Set this parameter based on site requirements.