Back up your Interface and WTF folders. After that delete the folders from your world of warcraft folder.
Download and exctract those folders from ArlenUI and put them into your World of Warcraft folder.
The font folder also goes in the main World of Warcraft folder.
Open the WTF folder and rename the following :
ACCOUNTNAME => to your account name.
ServerName => to your server name.
Charactername => to your character name.
At the character selection screen, make sure to enable Out of Date addons in the
Addon menu and enable all addons for your character.
When you login, go to ESC => Interface => Addons => and for each addon listed change the profile to ArlenUI.
For addons not listed:
/acb then change profile to ArlenUI
/suf then change profile to ArlenUI
/raven then change profile to ArlenUI (May need to disable WeakAuras first to open Raven Options)
/sldt global then copy profile ArlenUI
/grid then change profile to ArlenUI
/xloot then change profile to ArlenUI
For TidyPlates change the Primary and Secondary themes to ThreatPlates then type /tptp and change the
profile to ArlenUI.
If you don't want your cooldowns being announced to raid chat, open WeakAuras and disable the Announcements group.