SQL Server Management Studio 2018 delete the file C:Users\%username%AppDataRoamingMicrosoftSQL Server Management Studio18.0UserSettings.xml
SQL Server Management Studio 2016 delete the file C:Users\%username%AppDataRoamingMicrosoftSQL Server Management Studio13.0SqlStudio.bin
SQL Server Management Studio 2014 delete the file C:Users\%username%AppDataRoamingMicrosoftSQL Server Management Studio12.0SqlStudio.bin
SQL Server Management Studio 2012 delete the file C:Users\%username%AppDataRoamingMicrosoftSQL Server Management Studio11.0SqlStudio.bin
SQL Server Management Studio 2008 delete the file C:Users\%username%AppDataRoamingMicrosoftMicrosoft SQL Server100ToolsShellSqlStudio.bin
SQL Server Management Studio 2005 delete the file – same as above answer but the Vista path. C:Users\%username%AppDataRoamingMicrosoftMicrosoft SQL Server90ToolsShellmru.dat
These are profile paths for Vista / 7 / 8 /10.