How to change the mailboxes size in exchange 2007 or 2010?

1-    Check the mailbox sizes, you need to run this command from the Exchange Management Shell (EMS)

Get-MailboxStatistics -server servername | Sort-Object TotalItemSize –Descending | ft DisplayName,@{Label= “TotalItemSize (MB)”;expression = {$_.TotalItemSize.value.ToMB()}},ItemCount

2-    Check the mailboxes limit from the EMS

Get-mailbox -server servername| Sort-Object DisplayName | ft DisplayName, IssueWarningQuota, ProhibitSendQuota, ProhibitSendReceiveQuota