I need ti replace the timing belt (and waterpump?)

There is no such thing as a "How To" guide for this. You might find a generic video for timing belts in general, but that would be like watching a video on how to perform an operation on a person. You need to get very specific and read the guide for your exact engine. What you need is a copy of the manufacturer's service manual. That will have pages of instructions with line drawings, a page of all the special tools you'll need, and the critical torque specs for the bolts. Don't waste your money on Haynes or Chiltons manuals. Those only cover things competent do-it-yourselfers can handle, and a timing belt isn't one of them.

You do have one major advantage if you choose to tackle this job. Most import engines are of the "interference" design which means if the timing belt is off a few teeth, the pistons will hit the open valves and bend them. This happens real often when proper procedures aren't followed. Luckily your engine is not of this design, so you don't have to worry about bent valves.

The next thing is you'll want to buy a complete timing set, not just the belt. It will include tensioner and idler pulleys which do commonly fail leading to a shredded timing belt. Some tensioner devices include spring-loaded pulleys or spring-loaded pistons that develop added pressure from engine oil pressure. Whichever method is used, you don't want to risk destroying the new belt from reusing old mechanical parts. Also, when the water pump is run off the timing belt, if it's on the smooth back side, a belt that isn't adjusted properly or can't maintain proper tension can slip over the water pump's pulley, leading to overheating and serious engine damage. Here again, you don't have to worry about that because your water pump is driven by the toothed side. Still, the belt must be properly tensioned to reduce the chance of it jumping a tooth or two over one of the sprockets.

Once the timing belt is installed and adjusted, rotate the engine, by the crankshaft, two complete revolutions, then recheck the timing marks. Always rotate the crankshaft only in the normal direction, never backward, because some spring-loaded tensioner devices can be forced to retract when pressure from the belt is pushing it the wrong way.

There is nothing worse than having to do the job over again due to a mistake. To avoid that, I run the engine before I bolt on the covers and engine mounts. I want to see the engine start easily, sound normal, and idle smoothly, and I do not want to see any coolant or oil leaks. Once I'm satisfied there's no problems up to that point, I have the confidence to put everything else together, knowing that if I make a mistake now, I won't have as much to take apart again.