Hmmm. I'm a firm believer in the idea of each individual event having a profound effect on the rest of time. So i believe that for now, I'm still alive and well, so no, I wouldn't change the past. Everything happens for a reason and has its consequences, and I couldn't live with myself if I undid something that turned out to be very good, or helped along an even which was previously prevented which would tear things apart. Now, without consequences, would I? MAybe? Who knows?
i think that space travl is possible, but technology isn't powerful enough for us to find out how. & i think that you could go back into the past to revist memories, but not change them. but you could go into the future, & come back & prevent something bad from happening.