Changing hours to days on existing file

I am not normally in favour of running third-party content, particularly as I thought that surely, SURELY such a functionality would exist on MS Project. It makes no sense that using the Project Options and Schedule tab function to change duration units only works from when you start to add new tasks - I mean what happens if a planner from the supply chain issues a programme in hours or an exported file from another programme software imports in hours - how does this software perform if you cannot make a simple conversions to days, weeks or another unit of time!! Aaagh!

Anyway, in short, I followed and downloaded the macro as you suggested and it performs very well so a big thank you.

For anyone else reading this, there is also a work around (though I hate workarounds!) that other members of our planning team posted and which I have seen posted online.

STEP 1 - Click File, then Options, then Schedule. As other advice suggests, under 'Duration is entered in', select the duration unit you wish to convert to. Return to your programme by clicking OK.
STEP 2 - Right click against the current duration column and click Add a new column. Rather than select anything from the drop down list, just name the column 'Duration1' and it should standardise as a duration column with the unit you wish to convert to.
STEP 3 - Right click on the heading of 'Duration1' select 'Custom Fields'. Click on formula in the middle of the box and type [Duration]. Include the square brackets.
STEP 4 - Click Ok and OK on all remaining boxes to return to your programme. Duration1 should now match with the Durations column, but in the unit of your choice.
STEP 5 - Under 'Gantt Chart Format', uncheck the box for summary tasks in order to ensure they are now showing in your programme.
STEP 6 - Highlight 'Duration1' column and copy and paste this across to the Duration column.
STEP 7 - Delete Duration1 column and reinstate the summary bars by re-checking the box,

Voila.