Try
=TEXT(WORKDAY.INTL(DATE(RIGHT(A1,4),1,0),LEFT(A1,2),"0111111"),"mmmm/yyyy")
That's a neat formula, if the first week always starts on the first Monday of the year.
But if DowReena is using ISO-8601 as indicated, there is the additional requirement that Week 1 must contain the first Thursday of the year. So, for example, Week 1 2015 actually starts on Monday 29 December 2014.
B1: =DATE(RIGHT(A1,4),1,-2)-WEEKDAY(DATE(RIGHT(A1,4),1,3))+7*LEFT(A1,2)
C1: =TEXT(DATE(RIGHT(A1,4),1,-2)-WEEKDAY(DATE(RIGHT(A1,4),1,3))+7*LEFT(A1,2),"mmm yyyy")
Sheet1
<tbody>
[TD="bgcolor: #cacaca, align: center"]1[/TD]
[TD="align: center"]01/2015[/TD]
[TD="align: center"]Monday 29 Dec 2014[/TD]
[TD="align: center"]Dec 2014[/TD]
[TD="bgcolor: #cacaca, align: center"]2[/TD]
[TD="align: center"]05/2011[/TD]
[TD="align: center"]Monday 31 Jan 2011[/TD]
[TD="align: center"]Jan 2011[/TD]
</tbody>
DowReena, ISO-8601 doesn't provide any correspondence between week number and month. Jonmo1's and my formula give you the month of the Monday. So the second example above shows as January 2011, although 6 of the 7 days actually fall into February.