Changing Focus Keyword

Hello,

we managaed to rank really high (2-5 page 1) with a specific keyword. Sadly we ranked with the homepage because we made the mistake and gave the keyword 2 times.

Once for the homepage and one for a subpage about the keyword.

Now we want to rank the subpage and not the homepage which is ranking right now. Can I just delete the focus keyword from the homepage and switch it out? Does google switch the two pages then fast or will we lose rank and have to build it up again?