Write SQL query of Update using IF-ELSE MSDN/SQL

IF (select ColumnName from TableName where ColumnID=X) > 100

BEGIN
UPDATE TableName
SET ColumnName = 'Something'
WHERE CoumnID=Y
END
ELSE IF(Condition ........)
BEGIN
UPDATE TableName
SET ColumnName = 'Something'
WHERE CoumnID=Y
END
ELSE
BEGIN
UPDATE TableName
SET ColumnName = 'Something'
WHERE CoumnID=Y
END