How can I delete data?

Normally in Windows Explorer I have C storage and then I put external storage on D. The new drive still has 1 TB of old data on it and I have already deleted it all, but there are a few that cannot be deleted. (First of all, the drive is old and full of old Windows 8 stuff) There are programs, x86 programs, Windows etc. and for that I need trusted installer permissions. My question is, should I get the permissions and delete the data or will something on my system be changed or something, because I want to be really careful and maybe when the drive was plugged in it was connected to the system or something (I have no idea).