How doI evict my ex-girlfriend?

If she is not on the lease, then she will be consider to be a "licensee"; that is someone invited to enter and remain on the premises.  Now that her "license" (i.e. invitation) had been revoked she will need to be evicted if she will not voluntarily move out.  The question now becomes, who is the suitable party to file an "unlawful detainer action (i.e. eviction)?  To evict someone from their established home, the person who is entitled to possession of the premises must sue in court. If your ex-girlfriend has no lease, then you can file (however you must be certain that she in fact does not have one).  Even if her name is not on your lease, she could still be considered a "tenant".  For example, if the landlord has treated her as a tenant by accepting rent directly from her, by putting her name on the mailbox/doorbell, or if you and she rented the place together and it was clear that both of you were on equal footing.  Under such circumstances, she may have attained the status of a tenant. In that case, the landlord would have to file for the eviction because only landlords can evict tenants.

Assuming that she is a licensee and not a  tenant, so that you legally have standing to evict her, it is important to note that you must comply with all legal requirements.  Someone who is put out of his/her home in a forcible or unlawful manner is entitled to recover damages in a legal action against the wrongdoer. Additionally, using illegal methods to force someone to move is a criminal violation. So do not be tempted to use self-help measures such as removing her personal belongings or changing the locks.

At this point, you should consult with a landlord-tenant attorney or tenant's rights organization to figure out your ex-girlfriend's legal occupancy status  and just what are the legal procedures  for filing an eviction in your state.