Exchange 2010 Server Low On Space

As JoseO said best bet is to check for logging. If that is already on then you can do a few things.

You could create a new disk and move users as well to free up space just make sure the new database is backed up.

You could also check for disconnected mailboxes.
Get-MailboxDatabase | Get-MailboxStatistics | Where { $_.DisplayName -eq "<display name>" } | fl DisplayName,MailboxGuid,Database,DisconnectReason

This will list all mailboxes that were deleted but might still be in the 30 day recoverable time. those can be removed by running this:

Get-MailboxStatistics -Database databasename  | where {$_.DisconnectReason -eq "SoftDeleted"} | ForEach {Remove-StoreMailbox -Database $_.Database -Identity $_.MailboxGuid -MailboxState SoftDeleted}

I tried running the Set-StorageGroup -Identity "First Storage Group" -CircularLoggingEnabled $true but I received the following error

Here is results from your script

I found the method for enabling circular logging from the management console by going to
In the console tree, expand Server Configuration, and then click Mailbox.
In the work pane, right-click the storage group for which you want to enable or disable circular logging, and then click Properties. The <Storage Group Name> Properties dialog box appears.
Select or clear the Enable circular logging check box.

But I do not see Circular Logging as an option

OK try

Set-MailboxDatabase  -identity "Mailbox Database 0482295700" -CircularloggingEnabled:$true

Select allOpen in new window

Then unmount and mount the DB.

You have almost 1 TB of logs! Jezz