If you are uploading large files (>2gb) or a vast amount of smaller files via bulk upload and your account's used space hasn't adjusted after the upload, there are two ways to manually assess your used space.
Log in to your account and in the top right hand corner click the Refresh button. This will force your account to reassess the used storage and reflect the correct used space.
Reindexing your account is another way to force the account to take an inventory of all your data. Click Tools and navigate to the services section.
Once you are here click the Index Files button to begin the process.
A small window will pop up showing the progress and when it is finished it will display the image below.
Now your account is indexed and up to date!