For you to become an administrator, someone with bureaucrat access must make you one. On larger Wikia, there will usually be a community page for requests, with a page name such as "Prison School Wiki:Requests for adminship". On a smaller wiki, you may simply ask on the community portal or Forum, or ask a bureaucrat directly on his or her talk page.
If there are no active bureaucrats, use the "Requests for adminship" page to nominate users to become admins or bureaucrats. Once a community decision has been reached (or if there is no active community to debate the decision), please leave a message at the wiki adoption requests page and Wikia Staff can provide the rights.