FM doesn't work that way. You have to make your fields large enough to hold all of your data. In Layout mode, the Position Tab of the Inspector near the bottom you will see Sliding & Visiablity. Select Slide Up and Resize enclosing part. This will srink the fields to fit the data and slide following fields up.
FileMaker already does that. But the opposite way round from how you've expressed it. Fields move UP (i.e. squeeze to a smaller size) to take up unused space. This is done using Sliding fields. OR you can add scroll bars to fields so the user can scroll down to the bottom of the data in that particular record.
If this is for a print layout rather than data-entry, use merge-fields in a text block. You can make them as large as you need and set sliding/printing to make them reduce the part when not filled, or you can put them all in one large text block with returns between them, and the text block will auto-adjust.
I wish there was some way to make multiple fields adjust without getting in each others' way with data-entry fields, but it's usually print layouts where this feature is most important, and merge-text handles that nicely.
[When creating a text block on a layout in layout mode with the text cursor, see the menu item "Insert > Merge Field" to use this.]