On the login-page there is a "Forgot password" link, however this only works if the admin user is configured with an email address and an smtp-server is configured for Clerezza to send mails.

You can reset the password on the Clerezza shell (which is accessible without password on the console on which Clerezza is started) withe the following commands:
zz>import rdf.core.access.TcManager import rdf.core.access.TcManager zz>val tcm = $[TcManager] tcm: org.apache.clerezza.rdf.core.access.TcManager = org.apache.clerezza.rdf.core.access.TcManager@6de35b46 zz>import platform.Constants import platform.Constants zz>val sysGraph = tcm.getMGraph(Constants.SYSTEM_GRAPH_URI) sysGraph: org.apache.clerezza.rdf.core.access.LockableMGraph = org.apache.clerezza.rdf.core.access.LockableMGraphWrapper@39b7e5ee zz>import rdf.core.impl._ import rdf.core.impl._ zz>import rdf.scala.utils.Preamble import rdf.scala.utils.Preamble zz>val p = new Preamble(sysGraph) p: org.apache.clerezza.rdf.scala.utils.Preamble = org.apache.clerezza.rdf.scala.utils.Preamble@670583f6 zz>import p._ import p._ zz>import rdf.scala.utils._ import rdf.scala.utils._ zz>import rdf.ontologies.PLATFORM import rdf.ontologies.PLATFORM zz>val user: RichGraphNode = new PlainLiteralImpl("admin")/-PLATFORM.userName user: org.apache.clerezza.rdf.scala.utils.RichGraphNode = org.apache.clerezza.rdf.jena.commons.JenaBNodeWrapper@957eb29c zz>import rdf.ontologies.PERMISSION import rdf.ontologies.PERMISSION zz>user.deleteProperties(PERMISSION.passwordSha1) zz>user.addPropertyValue(PERMISSION.passwordSha1, "d033e22ae348aeb5660fc2140aec35850c4da997")
The above will set the password of the user admin to "admin". Replace the value of PERMISSION.passwordSha1 to the sha1 sum of the the desired password, which you may compute on a typical unix shell with: echo -n password | sha1sum