;with cteRowNumber as (
select COMPUTERNAME, SERIALNUMBER, USERNAME, LASTIP, LASTUPDATE, SOURCE,
row_number() over(partition by COMPUTERNAME order by LASTUPDATE desc) as RowNum
from YourTable
)
select COMPUTERNAME, SERIALNUMBER, USERNAME, LASTIP, LASTUPDATE, SOURCE
from cteRowNumber
where RowNum = 1
