Files can be checked out in the file thumbnail pane by users who have been granted upload/download permissions.
Checking out a file prevents the following actions by other users:
Downloading, copying, or deleting the file
Saving markup layers for the file
Uploading a new version of the file
The check-out can be cancelled by the person who checked out the document, a Project Administrator, or a System Administrator. Only the person who checked out the document can upload a newer version of the document to check it back in.
To check out/in a file:
Navigate to a project folder that contains the file you want to check out.
From
the file thumbnail panel, click on the check-out 
icon
for the file.
The area around
the thumbnail image changes to red and the undo check-out icon is
now displayed in the file details area indicating that the file is
checked out and locked 
.
Checked-Out File
Click the download
icon 
to
save a copy of the file you just checked out on your machine to make
the desired updates.
When you have finished editing the document and have saved your changes (using the same file name), click the Upload Files button in the file thumbnail panel where you have the file checked out.
Browse to the folder where you saved the new version and click the Upload Now button. The resulting window displays the file name in blue, indicating that it has been uploaded as a revision of a current document in that folder.
When viewing the
uploaded file version in the thumbnail panel, the version information
display's and the file is automatically checked in (the check-out
icon 
now
displays).
Check Out and In Multiple Files
To check out and in multiples files, select the checkbox next to all the files you want to check out or in and follow the procedures above.