• Go in the configuration manager and in the table of contents click “Links”.
• You are now in the section “Links”.
• Write _blank into the field Target window for external links

and that's all.

Other possible values for the target attribute are:

• _blank : open the link in a new window.
• _self or empty string : open the link in the same window.
• Other values such as _parent or _top or framename assume you are using a template with frames, in that situation, you should know what to put in this array.