This can be changed by adding an additional line to your config/site.php file.

Adding the following line to that file (before the ?> closing the php) .

would change the :: into a | . You can put whatever character you want to in there.

If, on the other hand you want to have a completely custom title. You need to add the page attribute "Meta Title" and put the title text you want in there.

Do this by accessing the page you want to change in "Edit" mode and then select the "Properties" button. Click the "Custom Attributes" tab and look for the field titled "Meta Title". If it is not there, simply add it by selecting Meta Title from the Add Attribute drop down.

Whatever you type into this attribute will be come that particular pages title.