How to manage partitions without booting into an operating system (something like a USB tool?)?

Yeah GParted is your best bet.

Of course, you need to be very careful when working with partitions as Adrian said. It is very, very easy to accidentally choose a wrong partition and delete your data.

Make sure you download the Live version. You can either make a bootable CD or a flash drive.

You can download and make a bootable disk or USB that contains the utility G parted partition master which also use as a similar to old can also be burned to a USB or disc which you boot to before your operating system loads to manage partitions and to delete them and to rebuild the master boot sector.

I'm not sure why you're asking that question. I put the new drive into a USB enclosure, and plug that into my Windows computer's USB port.

You're always going to have an operating system to do stuff.

You can use standalone partition editors like GParted:

https://gparted.sourceforge.io/display-doc.php?nam...

It is a live Linux CD boot distribution, but can be put onto a USB stick as well, with the proper tools.

Always remember, messing with partitions can destroy ALL your data, always make full backups before even starting such utilities...