We both wrote the examples with assumptions that you have only two patterns, if not you can go with the case stament itself

create table #SoftwareTest

(

SoftVersion varchar(500),

SoftVersionUpdated varchar(500)

)

insert into #SoftwareTest (SoftVersion)

Select '10.78.5'

union

Select '1.78'

union

Select '2'

union

Select '4.5'

union

Select '20.5'

union

Select '4'

union

Select '8.63.0'

union

Select '10'

union

Select '4.56.89'

union

Select 'NA'

union

select Null

update #SoftwareTest set SoftVersionUpdated=

case when CHARINDEX('.',SoftVersion,0) >0 then

substring(softversion,0, CHARINDEX('.',SoftVersion,0) )+ '.X'

when isnumeric(softversion)=1 then

SoftVersion + '.X'

else softversion end

select * from #SoftwareTest

drop table #SoftwareTest