Number of shards - a few question about it

Elastic Stack Elasticsearch
1

Hi,
i have three question about number of shards

  1. is possible to change number of shards of existing index ? Whether i must create new index and "copy" data?
  2. What are the recommendations: same number of shards for each index, or individually set number of shards for indexes
  3. Where i find informatiion/method/algorithm/tool to determine right number of shards?

Thanks in advance for info