You change it, there are couple of ways.
Method 1 using the GUI, this should be done by every user.
via site setting Site settings >> Click on Title, description, and
icon Link under "Look and Feel", Change the name and description as
per your requirements!
Method 2: You can use the powershell.
#Get the Web
$Web= Get-SPWeb "http://your-sharepoint-site.com"
#Set the Title & Description
$Web.Title = "Marketing Portal"
$Web.Description = "Marketing Portal"
#You can change the Quick Launch/Treeview navigation also (If its not a Publishing site):
$Web.TreeViewEnabled = $True
#Update the changes
Method 3: create an event receiver once a user provisioned his blog site your event fired and change the title according to your requirement.