I use Delphi 7 to develop programs, but the programs that I make, UI looks outdated. I was wondering if there is an option that I can adjust how to generated UI looks like?
It's not as simple as flicking a switch. Even in Delphi 7 there were component packs you could use, with theming. If you are not using anything like that now, it's not easily replaced.
If you want the more modern UI (note that the default controls are an older version), you'll need to include an application manifest. This will get you the modern control version, which will fit in with the OS themes that are consistent with Windows XP and beyond. Doing this will become more important if your app has any UAC considerations for the Windows that have that.
If you want something different than the OS, the answer above will be the only one you have.