Links created with the mouse or with the Link tool are always Finish-to-Start links. If you want a different type of link between two tasks, you will need to edit the link. Editing the link also allows the addition of lag time. Lag is used to delay the successor action (start of finish, depending on the type of link). Link type and lag are both found on the Edit Dependency dialog box. Remember that a negative lag time allows tasks to overlap.
Editing the Link Type
Position your mouse pointer over the link you want to edit. You will notice that the ToolTip that comes up will contain information about the link.
Double-click the link to open the Edit Dependency dialog.
The dialog shows the names of the tasks that are linked with this dependency. Make sure you are editing the right link.
The Type drop-down list contains the four link types. Choose the link type here.
Enter the Lag (positive number) or Lead (negative number) value for the dependency here.
To delete the link between these two tasks, click the Delete button.
For Your Information
Entering Lag as a Percentage
By default, lag is entered in days, but you can also enter it as a percentage of the predecessor task's duration. To do this, open the Edit Dependency dialog and enter the desired percentage of the predecessor's duration in the Lag field, followed by the % symbol.
Position your mouse pointer over the link you want to edit. You will notice that the ToolTip that comes up will contain information about the link. 
Double-click the link to open the Edit Dependency dialog. 
The dialog shows the names of the tasks that are linked with this dependency. Make sure you are editing the right link. 
The Type drop-down list contains the four link types. Choose the link type here. 
Enter the Lag (positive number) or Lead (negative number) value for the dependency here. 
To delete the link between these two tasks, click the Delete button. 
