If you are using resources on your projects (not everyone does), resolving overallocations is one of the most important things you will do to keep your schedule in a realistic state. Anyone can just assign resources here and there without paying attention to allocation levels, but this creates schedules that are impossible to achieve and thus practically useless. Making sure that your resources are not overallocated is a key part of managing your schedule. This section covers how to find overallocations and how to deal with them through leveling delay or work redistribution.
Resolving an Overallocation by Adding Leveling Delay
Examine the slack for the task in question.
Decide whether there is enough slack, or whether delaying the project is acceptable to resolve the overallocation.
Delay the task by adding the required number of days in the Leveling Delay field.
The 8- hour assignment and the task's Gantt bar move out by the number of days entered in the Leveling Delay field.
The green line represents the number of days of leveling delay for the task.
This change resolves all overallocations for the resource, as the name is no longer in red.
Did You Know?
You can erase any manually entered leveling delay values . You can do this by using the built-in resource leveling features of Project. Just click Tools, Level Resources, Level Now, or clear leveling values by clicking Tools, Level Resources, Clear Leveling.
Resolving an Overallocation by Redistributing Work on the Assignments
Examine the amount of slack for the tasks. In this case, there are two days of slack for Brian's tasks .
If there is enough slack or if delaying the project is acceptable, edit the hours in the upper pane to values that add up to less than a 100% assignment.
Changing the hours to four per day for two days for each task lowers the allocation to 100% for each day.
This has the effect of lowering the Assignment Units to 50% for each task and increasing the duration to two days.
Examine the slack for the task in question. 
Decide whether there is enough slack, or whether delaying the project is acceptable to resolve the overallocation. 
Delay the task by adding the required number of days in the Leveling Delay field. 
The 8- hour assignment and the task's Gantt bar move out by the number of days entered in the Leveling Delay field. 
The green line represents the number of days of leveling delay for the task. 
This change resolves all overallocations for the resource, as the name is no longer in red. 
