Hi @K.mitch 
Do you want to change the layout by increasing the group code filed or do you want to increase the length of the filed to increase more characters in it?
If you want to adjust the layout, you can do it through the layout property. (as shown below)

If you need to increase the length of the database or client end, then you need to do it as a customization change. 
Hope this info helps.

@K.mitch I don’t think you can change the Character Length in Basic Data or any as it needs to fix all the places it used. 

Thanks Both - It’s the actual number of characters in the field I need, i suspected i wouldn’t be able to do it but it was worth the ask.  :)   

it can only be done by modification. But not recomended. Everywhere it had been fetched into and referenced form must be enlarged and that is the other word of creating a buggy system. Instead you can create custom field marked as public and hold extended info there, add reference custom fields on entities where needed  on screen or report layout.