My pc has both W10 and Ubuntu.

Left to itself on start it defaults to W10

 

I wish it to default to Ubuntu.

 

My pc   has an I9 intel processor.

I hope its just a question of pressing the correct 'F' key on start up.

Suspect that I can figure it out from there.

F2 and F12   do not seem to work.

 

Can anybody help?

Do you use two SSDs or HDDs?

If yes, then you can do it in the BIOS.

 

If you have just one SSD or HDD then you can't do it in the BIOS. Then google boot-manager.

I have W10 and Linux installed on one SSD. On boot up I am given the option as to which OS I want to use.

RUN - "msconfig"

 

If you have more than one operating system you'll have the choice of setting "Default"

 

 

 Thanks to all those who   have replied.

In the event I discovered a Linux program called 'Grub Customizer'.

I downloaded this via terminal.The input command   came from a  Ubuntu  help web page.

With that in place it was  fairly straight forward.

The program has other features.