If an employee leaves your company and is replaced by another employee, it is a best practice to deactivate the old user and create a new user. Please never just exchange the username and email address.
To deactivate the login for a User
1. Click Setup | Manage Users | Users.
2. Click the checkbox next to the user's name and click the freeze button. (Stops the session if they are logged in)
3. Click Edit next to a user’s name.
4. Deselect the Active checkbox and click Save.
Even if the user is deactivated, his license for Propertybase is still active. To remove the users license, to enable Propertybase for another user;
1. Click Setup | Build | Installed Packages.
2. Click on the link "Manage Licenses" next to "Propertybase"
3. Click on "Remove" next to the user you have deactivated
If this is an Admin user please see the How to change your Administrator Access article
Processes running with an Inactive User
There is things to consider after you have deactivated a user that the system does not alert you about. You will need to change all Action Plans, Workflows, Process Builder, Dashboards as running user and Front Desk going to the user. Each one will fail if they do not have an active user.
Transferring Records to a new User
If by any chance that the user has deleted any records before they left make sure you check the Recycle Bin. Go to any object and check on the left side bar at the bottom. If you don't see a left side bar make sure you expand it.
Here is some more documentation on the Recycle Bin