How to channel Redstone current vertically?

Going straight up is one of the easier directions to manage via redstone.

Just alternate torches and solid blocks, and you can send the signal up as far as you need.

You can place redstone dust on glowstone and upside-down slabs. This is important because they are also transparent blocks, so the redstone current won't be blocked. You can set up your glowstone or top slabs in an alternating pattern, with redstone on top, and then run the current from there.

And here is a video by CaptainSparklez that demonstrates this:

In this specific case with powering two vertically stacked pistons, you can use the Redstone Torch stacking technique, and it works out nicely. The torch adjacent to the bottom piston powers it, and also powers the block above it, powering the top piston as well. Conveniently, there's no need to invert your input because of the even number of torches used for the vertical signal transmission.