Preface: when it comes to installing operating systems I am a script kiddie. Every time I find a solution to some problem I am so happy I want everyone to know. This is why I am publishing this post, although, as you will see, all of the merit goes to a “mysterious” user of askubuntu, anwar.
I was in a situation in which I had an old laptop with a small partition reserved for Linux Ubuntu and a large one for windows.
I decided to give the PC to my mum, who will never use Ubuntu, and she likely would have troubles in managing dual boot.
Thus, I set out to remove grub.

Note: I do not have any install disk, nor recovery disk. Maybe I had them, once, not sure. In case you have a recovery disk, then things are easier.

Luckily enough, I found the answers here on askubuntu (answer by Anwar):

I repost it (with minor modification), in case somenone else may need it.

1) First download bootsect.exe from here into the Download directory (Warning the download will bring you through some redirection, but at the end you will get the program).
2) Rename the file to bootsect.exe (the name should be _Getintopc.com_bootsect.exe)
3) press the windows key, type cmd.exe and on the result (The command prompt) start it as an “Administrator” by right clicking on the cmd icon, and select Run as Administrator.
4) In the new cmd.exe window, cd to your download directory. for example cd C:\Users\Lalu Patel\Downloads. _assuming your user name is “Lalu Patel”.
5) Then enter this command. bootsect.exe /nt60 ALL /force /mbr.
6) Restart your system to see that, Windows is automatically loading without grub.

At this point, if you need to resize your partition, just go to askubuntu and follow the instructions