Joint tenancy means that you and one or more other persons share interest in the same property with a right of survivorship, i.e. if you die, the other person will inherit your share of the property (husbands and wives generally are joint tenants when it comes to property ownership).

Tenancy in common means that each of you owns a particular share, and you can sell your share to someone else, or will it to someone and it is exclusive from the other person's share. Imagine a single property with four equal partners, each with their own deed representing 25% of the interest (although the division may be any %)

To change from joint tenant to tenant in common you can sell your interest in the property, at which time a tenancy in common is created... here is a great outline from About.com that describes the various situations in greater detail:

If one of the joint tenants sells or conveys the interest created in a joint tenancy to another person, the joint tenancy is broken, and a tenancy in common is created. Joint tenants cannot stop another tenant from breaking the joint tenancy.

To dissolve the tenancy in common,

• One or more co-tenants can always buy out the others.

• The property can be sold and the proceeds distributed equitably among the owners.

• A partition action can filed. This involves going to court and asking to sell the property under court order and distribute the proceeds among the owners. When a co-tenant dies, you may see a partition action filed when an heir may want to sell and the other co-tenants do not.

The exact circumstances that are necessary to satisfy both joint tenancy and tenants in common may differ from country to country, but the About.com (U.S.) definitions are consistent with what I learned when I studied Real Estate in Ontario, Canada last year.

Hope this helps!