Hello. Sometimes while playing a video it happens to go back by pressing unintentionally the return/back button of my remote controller, and I have to press the same button different times until I go back to the video.
Is there any way to change the way to go back to menu?
Something like having to keep pressed back/return button for few seconds or pressing it twice in a second would be great.
I hope you can help me.
Thanks 
You can invoke a fullscreen action to return to a music or video file playing in the background. If you have an OSMC remote this can be done from most screens by holding down the home button. If you have some other remote then you can use the keymap editor to map a key to this action.
In Kodi most remotes have only a simple single press action. Some, like the OSMC remote have short and long presses. There is no pressing twice action available in Kodi.
I use my TV remote controller via Hdmi-Cec.
The long pression is fine for me. Can you tell me how can i set it?
CEC does not support longpress. You probably also have very limited buttons available to you as well. Your options without changing remotes would be to download the keymap editor add-on and use that to map one of your buttons that are currently performing some other function to fullscreen under global, or else I can walk you through disabling the back function so the only way to exit out of a playing video is to press stop. The latter would involve a bit of command line editing though.
In case you’re using the OSMC Skin, you may simply open the side menu and click on the fullscreen playback button you’ll find there. That should be pretty quick as well 
CEC does not support longpress. You probably also have very limited buttons available to you as well. Your options without changing remotes would be to download the keymap editor add-on and use that to map one of your buttons that are currently performing some other function to fullscreen under global, or else I can walk you through disabling the back function so the only way to exit out of a playing video is to press stop. The latter would involve a bit of command line editing though.
I think it’s fine just pressing STOP. Can you guide me please?
First access the command line which you can find instructions for in the following wiki
Once there you will need to make a custom keymap with the following
nano ~/.kodi/userdata/keymaps/gen.xml
In the text editor that opened you will need to enter the following EXACTLY as seen here. Any mistakes will likely keep it from loading.
<keymap>
<FullscreenVideo>
<keyboard>
<key id="216">noop</key>
</keyboard>
</FullscreenVideo>
</keymap>
Once you have done that you can save it with ctrl+x, y, and then enter. that is all there is to it other than restarting Kodi so the keymap loads. Do note that if you do this don’t ever open the keymap editor addon as it doesn’t understand the noop action and will remove it.