You can shift without the clutch, as long as you match "engine speed" to "road speed." That is what happens when truck drivers "double clutch." You can shift without your clutch as long as you "match" the rpm's with the speed you are travelling. You just might have to pull the shifter out of gear, goose the accelerator, and then feel the way into the next gear as the rpm's drop. It is the opposite for downshifting.

With today's transmissions, however, it is not very effective to do this with your car. Synchros help out quite a bit.

David Liske