How to change background without affecting the other elements?

[Adooby-doobie]

Hello everyone

I wanted to change the blue background and tried using the hue/sat layer to do so. But it doesn't work well. How do I achieve it?
Please help
Thanks

 

[c.pfaffenbichler]

I think the separation may not be good enough. 

But the HSB/HSL Filter might be helpful. 

[Adooby-doobie]

What steps did you use for this?

[c.pfaffenbichler]

See screenshots