ITIL admin role -Possesses more privileges than the itil role and is intended for team leads. This role can delete incidents, problems, changes, and other related entities when both the itil and itil_admin roles are assigned.

ITIL role -Can perform standard actions for an ITIL helpdesk technician. Can open, update, close incidents, problems, changes, configuration management items. By default, only users with the itil role can have tasks assigned to them.

Check this link for more details :

https://docs.servicenow.com/bundle/helsinki-servicenow-platform/page/administer/roles/reference/r_Ba...