How do I remove the excess white space from the values in my SQL table?
The first thing you should do is change the datatype of the column to nvarchar(200),

The char and nchar datatypes are intended for data that is more or less fixed length. Your example shows that you are not dealing with fixed length 200 character strings.

Currently each instance of the 'Logged in' string takes 400 bytes. Stored as nvarchar it will take 20 bytes (and 11 as varchar).

Then you can RTRIM in an UPDATE statement to remove the trailing spaces.

NB: In some circumstances you might find that creating a new table from scratch actually works better than the above as the insert can be minimally logged and it doesn't copy the data once and then trim it. It also ensures that no space is consumed by the dropped column. You can use the SSMS table designer to generate the script for this and then add a RTRIM to the result for something like the below.

SET XACT_ABORT ON;
BEGIN TRANSACTION

GO

CREATE TABLE dbo.Tmp_YourTable
  (
     /*Other columns*/
     YourColumn NVARCHAR(400) NULL
  )

GO

INSERT INTO dbo.Tmp_YourTable WITH (TABLOCKX)
            (YourColumn)
SELECT /*Other columns*/ 
       RTRIM(CONVERT(NVARCHAR(400), YourColumn))
FROM   dbo.YourTable WITH (HOLDLOCK TABLOCKX)

DROP TABLE dbo.YourTable

GO

EXECUTE sp_rename
  N'dbo.Tmp_YourTable',
  N'YourTable',
  'OBJECT'

GO

COMMIT