Your IT guy is still out of the office? He can't assist you? Because remote help in those cases (this has little to do with LS, but with using programs and computers in general) is very difficult.
I will try and see what we can do from here.
This is how it look for me, when I open the en.po file with PoEdit:
You see the base string in the left column, as it should appear now in your Limesurvey installation. In the right column, there would usually be the translations for other languages. But for obvious reasons, in the English version, there are no translated string.
I have never done this for the English version, but if you now search for the string that you want to change, you can then insert your modified string in the lower text box and it should appear in the right column. Then save it and upload it into the right folder of Limesurvey. Then the changes should be applied.
However, I strongly recommend to make such changes in a test environment first (this is considered a good practice), and only upload it to the productive system (the server where you want to run the surveys on) once you are sure that it is what you want. And make backups from the original files, so that you can go back in case you did something wrong and get lost.