I have dual booted windows 10(in c drive) and ubuntu 19.10(in e drive) .
I need to remove windows 10 and start working in ubuntu.so how do i remove windows 10.
Will it also remove the grub boot loader ?
In your other thread you ask about which operating system(s) would be good for your Lenovo laptop. Since you are open to the idea of erasing everything... that is the fastest and easiest way to get rid of your Windows 10.
With whatever version of Linux you decide to try, during the installation (at the partitioning step)... tell it to "Use Entire Disk" and then it will completely erase Windows and install Linux as the only system. This eliminates any possibility of the GRUB bootloader getting confused.
I will make some distro suggestions in the other thread.