How to clean re-install Windows 10 Single Language on my Lenovo Laptop

I have Lenovo G50 70 with Windows 10 Single Language on Partition C (Upgraded from Windows 8.1). I want to re-install Windows 10 SL as my Laptop has become very slow. I have Windows 10 SL on DVD as well as on USB Pendrive which I had downloaded as ISO from Windows 10 website. Now I would like to know - how to re-install the same which does not cause me any problem as far as activation is concerned and it should be a clean re-install. Please advise me step by step. At the time of reinstallation - will I have to opt for " formatting my C drive".
My internal hard disk is password protected which I could not remove. I had tried many times by going into the bios but the option to select Admin Password and Harddisk Password could not be done. The up and down keys just do not navigate to these options. Any help in this regard is most welcome.
Therefore will it cause any problem at the the time re-installation of Windows 10 Single Language.?
Please help me re-install my Windows 10 SL.
Thanks in advance
Ashok Kumar Bagaria

If the operating was upgraded during the free period you should have a digital license.

Many problems with the operating system can be fixed by performing an in place upgrade repair.

If there are registry problems then you can consider a clean install.

Another option to consider is using Macrium to make a backup image.

There may be others that can guide you on the password problems.

Clean Install Windows 10 Installation Upgrade Tutorials

Repair Install Windows 10 with an In-place Upgrade Installation Upgrade Tutorials

Backup and Restore with Macrium Reflect Backup Restore Tutorials

zbook said:

If the operating was upgraded during the free period you should have a digital license.

Many problems with the operating system can be fixed by performing an in place upgrade repair.

If there are registry problems then you can consider a clean install.

Another option to consider is using Macrium to make a backup image.

There may be others that can guide you on the password problems.

Clean Install Windows 10 Installation Upgrade Tutorials

Repair Install Windows 10 with an In-place Upgrade Installation Upgrade Tutorials

Backup and Restore with Macrium Reflect Backup Restore Tutorials

Thanks for prompt response. I will go through these links and choose an option best suitable for me.