Option A:

1- Go to Sales Forecast

2- Search by name for the Lead

 3- Click Edit/View

4- Check/Edit the Expected Closing Date

Option B:

1- Go to Lists & Contacts then choose Desired List 

2- Search by name or number and find the desired lead

3- Click on Open Lead 

4- Select Sales Forecast and check Expected Closing Date 

To Edit:

5- Click More Actions and edit the required date