Changing boot drive and formatting

[pumped]

I've bought an SSD and I am moving my PC parts into a new case and wish to format my current hard drive, which at this moment contains the OS, and obviously install the OS onto the SSD when I install the two drives into the new case by a fresh windows install. I'm wondering how I am meant to format the hard drive to allow for a fresh windows install onto the SSD, while its currently still in use and running my OS. I was going to format the hard drive just before moving the parts over, by disk management, and then installing both drives into the case then using an install USB for windows to get the OS onto the SSD, however I'm unsure if this is the best way to go about it, as surely I cant fully format my hard drive while windows will be currently running off it. 

[spartaman64]

you dont have to format the drive to install windows its going to format automatically

[pumped]

14 minutes ago, spartaman64 said:

you dont have to format the drive to install windows its going to format automatically

Will the hard drive format though? My OS is currently installed on a nearly full HHD but I'm going to add an SSD which I will install Windows onto through USB, will doing that also wipe the hard drive automatically?

[spartaman64]

3 minutes ago, pumped said:

Will the hard drive format though? My OS is currently installed on a nearly full HHD but I'm going to add an SSD which I will install Windows onto through USB, will doing that also wipe the hard drive automatically?

no you have to format/wipe that yourself. you can do it in the windows usb installer