When Samsung releases it (and your network approves it assuming a locked phone here), you shall have your update.
Go on sammobile, search software, type model number (like SM-G920F) and the latest software will be revealed.
Please see Tim's post above yours. Until Samsung releases the update and it is approved by your carrier (assuming a carrier-branded device) you won't get an update. Once it's available, tapping on the option in settings to check for updates will reveal it for installation