Is there a simple way to toggle kicad layers? For now, I am able only to manually tick the respective layer boxes. Is there a way to optimize this task, e.g. layer profiles?

In the PNS router, before you begin placing a new track, press the v key to toggle between your paired layers. Correspondingly, after you begin laying the track, v will place a via (and switch you to the paired layer).

If you wanted to switch to a specific layer, the default hotkeys are:

• Top Copper -- PgUp
• Bottom Copper -- PgDown
• Inner Layer 1 -- F5
• Inner Layer 2 -- F6
• Inner Layer 3 -- F7
• Inner Layer 4 -- F8
• Inner Layer 5 -- Shift-F5
• Inner Layer 6 -- Shift-F6

You can shift up and down layers with + and -

• Can you change the layer of a track you just started (and realised it should go to a different layer) without aborting routing first? – silverdr Sep 23 '18 at 12:58
• @silverdr No, because the routing is explicitly tied to the starting net and its associated layer – Seth Sep 23 '18 at 16:23
• this is kind of disappointing. "The other software", which I am now in the process of leaving behind makes no problem with that. You start routing, you realise you used the wrong layer so you change it on-the-fly with one click. I get that KiCAD still doesn't allow that. – silverdr Sep 24 '18 at 17:32