Purging Loki, amd Loki Metrics

Good morning, i have two questions:
First of all, when i change the format of the log sent to loki, how is it possible to purge all the older logs ?

Second, is there a way to get internal metrics such as olded logs stored ?

In prometheus there is prometheus_tsdb_oldest_timestamp_seconds for exemple which return the epoch timestamp or the oldest stored entry.

How is it possible to know if my stored logs are 1 day old or 7 days old ?