Not within Syntronik, I think you would do it in Explorer / Finder.
Disclaimer: I have not tried deleting these sorts of folders / files so it may cause problems. Proceed at your own risk and only if you understand fully what you are doing.Here, the files are in:
L:\IK Multimedia\Syntronik 2\Instruments
L:\IK Multimedia\Syntronik 2\Samples
L:\IK Multimedia\Syntronik 2\Library Info
L:\IK Multimedia\Syntronik 2\Library Resources
and
L:\IK Multimedia\SampleTank 3\Instruments
L:\IK Multimedia\SampleTank 3\Samples
L:\IK Multimedia\SampleTank 3\Library Info
You will probably need to do a Rescan in the Preference Settings / Library. And, it may be easier to recover if you move the appropriate folders / files to a different location, rather than just delete them.