What you're looking for is a Merge, for the insert/update. Here is an example that should help you:

Create table #Test (CustomerID int,

Name varchar(20),

City varchar(20));

Insert into #Test

Values (1, 'Steve','London');

Select *

from #Test;

MERGE #Test as Target

Using (Select 1, 'Steve', 'Colchester') as source (CustomerID, Name, City)

On (Target.CustomerID = source.CustomerID)

when matched then

update SET Name = source.name,

city = source.city

when not matched then

Insert ( CustomerID, Name, City)

Values (source.CustomerID, source.Name, Source.City);

Select *

from #test;

MERGE #Test as target

Using (Select 2, 'Donna', 'Leeds') as source (CustomerID, Name, City)

On (Target.CustomerID = source.CustomerID)

when matched then

update SET Name = source.name,

city = source.city

when not matched then

Insert ( CustomerID, Name, City)

Values (source.CustomerID, source.Name, Source.City);

Select *

from #Test;

Drop table #Test;