How to time travel?

The only known way would be a MATHEMATICAL solution of Einstein’s general relativity called a closed time-like curve (CTC)

A CTC has interesting properties. It starts and ends at the same point in spacetime so it looks like a big loop in spacetime, starting at one point of spacetime and ending at the same spacetime point. So, someone traveling the CTC will have the same spacetime point both in their past and in their future. 

If the intrepid traveler watched their wristwatch during the trip, the wristwatch would look normal, ticking way as it normally does so the traveler is always traveling toward their future as they traverse the CTC. But the direction of their future is changing as they follow the CTC, ultimately arriving back at the same spacetime point as they started from. So, you have the interesting fact that the traveler will always think they are traveling toward the future on their trip to the past !

The solutions of general relativity that contain CTC’s are likely idealizations that can’t occur in nature, but who knows. Recent papers have shown that no paradox would occur in CTC’s although I’m not convinced on that point.

Just sit down and you will travel forward in time 

build a spaceship and travel as fast as you can.

it will only slow time for you and you could return to the future.

going to the past is unlikely to be possible.

Close your eyes and count slowly to sixty. You just traveled one minute into the future. There's no going back.