This is same case of mine. So I guess you have hp laptop. If this is the case then open you BIOS menu by pressing F10 at startup. Then go to boot options or might be system configuration. There you can see boot options
Then press Enter. There will appear two option.
- Widows Boot Manager (llike similar)
- Ubuntu
After that this will appear
Well I missed a thing. Here in Uefi boot order there is OSBoot manager. Press Enter.
Then press f5 or f6 that will change the preferences. Here I have Windows as my first preference. You should place windows option at second place by pressing f5 or f6.
Then press f10 for save and exit.
Hope that helps