VBA for MS Access – How to Maximize Access Application Main Window

I think I can guess why your VBA is only changing around 150 records instead of all of them, but more importantly, you need to know that the specific method you're using--changing all the fields using VBA--can lead to incorrect data in your table. And, you can accomplish what you want much more easily with a SQL query ... even one made using the query designer. But for now I'll stick with plain SQL. There are three possibilities and corresponding approaches:

1 You just have to change a limited number of different sizes from mm to European. In that case use the switch function, e.g.:

update BS_2704
set Sizes = switch(
  Sizes = 150, 24
, Sizes = 160, 25
, ...
, Sizes = 325, 50
, true, Sizes
)

2 You can use a mathematical formula to convert from your mm size to your European measure, e.g. like http://en.wikipedia.org/wiki/Shoe_size#Europe:

update BS_2704
set Sizes = Sizes * 3 / 20

3 You can't use a mathematical formula, and you have such a large number of conversion mappings that putting them all in a single switch function is unwieldy: in this case you create a new table, e.g. named tblSizeMappings, with the mm sizes and the corresponding European sizes:

SizeMM SizeEuropean
   150           24
   160           25
   325           50

Then, do an update query like above but using the tblSizeMappings table to get the European sizes:

update BS_2704
inner join tblSizeMappings
on BS_2704.Sizes = tblSizeMappings.SizeMM
set BS_2704.Sizes = tblSizeMappings.SizeEuropean

You need to add:

On Error Resume Next
DoCmd.Close AcQuery, "QueryFromMasterSearch"
On Error GoTo Run_Click_Err

just before you open the query.

So, your code becomes:

Private Sub Run_Click()
On Error GoTo Run_Click_Err

    On Error Resume Next
    DoCmd.Close AcQuery, "QueryFromMasterSearch"
    On Error GoTo Run_Click_Err
    DoCmd.OpenQuery "QueryFromMasterSearch", acViewNormal, acReadOnly

    Run_Click_Exit:
    Exit Sub

    Run_Click_Err:
    MsgBox Error$
    Resume Run_Click_Exit

End Sub

The On Error Resume Next bit tells Access to not worry if the Query Window is not actually open. If you left that out, and didn't have the Query Window open the code would spit out an error.