Where is my root folder and how to delete old unused projects?

Hi I have tested quite often UE up to 5.4 now.

Since then I managed to upgrade to my 12GB GPU card and 256 GB of memory ram and work directly of 2TB of DDR Samsung . Before I worked via normal hard disc which slowed everything very much.

I just finished my model from SKU to Twinmotion 25 1/1 done all the lights etc.

I would have liked to add more trees but it sent my % spiraling up to 100%
( I have four crossing streets with planters designed to hold trees and make my game space
a green line space)

I have many characters in my TM file that I used to do many renders
I will not really need them all in my UE game template file.
Do I delete them all in TM or rather later in UE.

I have deleted the initial terrain because I still can’t figure out how to cut out a square
for it not to interfere with my model

Can I add land and sculptable terrain within UE without it cutting through my model?
it is 8 floor deep underground and 11 over ground.
I need to cut away any land at street level in an exact square shape

My game should be populated by avatars/ gamers/ players

As I need to export my Datasmith file, I am asked to point at the root directory of my project.
Which I can’t locate, maybe a stupid question I must admit.
Watched tutorials but they go to the root directory as if it was nothing special no one explains
how where and why it is located here or there.

My Twinmotion file has a new file name and is 5GB in size.
I would like to do like a spring clean and delete seven or all previous files and start from scratch I have NO need for them at all.
I don’t know if I can or need to delete the “MyProject”
My new disc is called G and J is not where I work from anymore

Is there another format to import from Twinmotion to UE 5.4 ?
Can it be done by FBX format?