TSQL updating/deleting from JunctionTable

I'm having difficulty figuring out the correct way to manage the following scenario.

I have 3 tables Categories, Listing, Junction

I'm using the Junction table for many-to-many relationships between my Categories & Listing tables, as any given record inside my Listing table can be assigned 1 or many Categories from the Categories table.

I've figured out how to INSERT correctly into both. Now my predicament is Updating.

If a user wants to Update their Listing to new categories then my code needs to delete any existing records in the JunctionTable and replace with new ones. How can I write a SQL statement that accomplishes that?

These are my two insert statements that fire when i'm adding a listing.

INSERT INTO BND_Listing_testing

(Company,Doors,Address,Address2,City,Region,Country,PostalCode,Lat,Long,Phone,Fax,Website,Description,Actualized,Verified,IMG1,IMG2,IMG3,IMG4,DateAdded)

VALUES

('[Company]','[Doors]','[Address]','[Address2]','[City]','[Region]','[Country]','[PostalCode]','[Lat]','[Long]','[Phone]','[Fax]','[Website]','[Description]','[Actualized]','[Verified]','[Image1]','[Image2]','[Image3]','[Image4]','[DateAdded]')



select scope_identity()

DECLARE @CatIDStr VARCHAR(100) = '[CatID]',@CatID VARCHAR(100) = ''



WHILE LEN(@CatIDStr) > 0

BEGIN



   IF CHARINDEX(',',@CatIDStr) = 0

   BEGIN

      SET @CatID = @CatIDStr

      SET @CatIDStr = ''

   END  

   ELSE

   BEGIN

     SELECT @CatID = SUBSTRING(@CatIDStr,0,CHARINDEX(',',@CatIDStr))                                        

     SELECT @CatIDStr=SUBSTRING(@CatIDStr,CHARINDEX(',',@CatIDStr)+1,LEN(@CatIDStr))

   END



   INSERT INTO BND_ListingJunction_testing (Junc_LID,Junc_CatID)

   Values ('[ScopedLID]',@CatID) 



END