Apple isn't expected to release its latest software update, iOS 14, until the fall (likely mid-September), but if you want try it out and access all of its cool features, such as Home screen widgets, picture-in-picture video calls, and threaded iMessage conversations, you can -- you just have to download the public beta for iOS 14, which is available now.
First, a word of caution: It's called a Beta because it's not fully cooked. Bugs abound, and you should know that installing it on your main device is asking for inconvenience so maybe think twice. If you do decide to go ahead, backup your iPhone beforehand. Things can go wrong and you could potentially lose things like photos, iMessages and number of things that you hold dear.
To backup your iPhone, connect it to your Mac or MacBook via a charging cable, open Finder, select your iPhone in the sidebar on the left, and select the option to backup your iPhone to your computer.
Once your iPhone is completely backed up, disconnect it from your computer and open the link to Apple's Developer Program enrollment website -- here -- and click the big blue button that says "Sign Up." From there, you'll have to log into your Apple ID, agree to some special terms, select "enroll your iOS device" and then selecting the "Download profile" button on the following page. Finally, open your iPhone's Settings app, select General and the beta software will be located in the Software Update section.
Install it and you should be good to take on the iOS 14 beta.