Change retention time on prometheus

So I am running Prometheus on an Ubuntu server and started running it a while ago by just running

sudo ./prometheus

However, I wanted to append

--storage.tsdb.retention.time=1y

to the end of this command. How can I change the storage retention time of a running Prometheus process without stopping Prometheus from collecting metrics. It is very import that I change the retention time WITHOUT losing the metrics that Prometheus has already collected on this server. Please let me know anything that might help. Thank you.