How can I refresh the analytics (open rate, click rate, etc)?

All you have to do is click on either the open rate, click rate, or unsubscribe rate in order to refresh the stats:

The reason those numbers aren't populating automatically is because after switching to Sendgrid recently we saw that if we request those stats too frequently the Sendgrid API starts blocking our requests.  We will eventually add some logic in to update those stats automatically but it's fairly easy to just refresh them manually for now.

Also, once we add the logic to refresh the stats less frequently, it's likely we'll refresh them on a daily basis, so you will likely want to still refresh them manually any time that you check up on them, since they will probably be several hours old at that point.

Here's the trello ticket that you can upvote to expedite this feature:

https://trello.com/c/PF0spIu0/86-refresh-sendgrid-stats-automatically