[Mart]

The crucial bit of info that you might be missing is that you have to move the guide down first. That will free up the uppermost clip. Once the clip is removed the whole assembly can be removed in an upwards direction.
The problem is that the guides are so tight that the normal pickle fork valve tool can't get enough grip on them to pull them down.
I have had good luck using a tyre iron down the intake ports to push the guides down. Horseshoe clips are then removed and the valve removed upwards as stated.

If you can't move the guides down you can try lifting the spring and removing the valve retainer. then lift the valve as far as it will go and yank the spring out of there. Then you use an "onion" tool to go around the valve head and knock the guide down.
Yank the horseshoe clip out and either push the guide up or sometimes you can continue knocking the guide all the way down until the two halves fall out below.

You need a selection of valve compressor tools, pickle fork levers, onion tools, hooks, plus I also have a specific flathead valve removal tool. That is like a big C clamp. It still relies on the horseshoe clip being removed though.

There is also a special spike that is used to yank the horseshoe clips out but that can be hit and miss.

First and foremost try a tyre lever down the intake ports, it is a great labour saver.

If any of the videos you watched were from Mart's Garage that was me.

I have showed valve removal many times.

Some people just launch straight in with the cutting torch but I try and save what I can.

Good luck with it.