By default, report table widgets are full-width and cannot be resized. This is to allow them to automatically adjust to the required table length without affecting any widgets below the table.
However, you can allow tables to be resized manually by opening the widget settings and changing "Dynamic Height" to "No".
Where to start
Open the report widget settings for the table widget you'd like to change. Look for the option "Dynamic Height", and set it to "No".
Then click "Save Settings" at the bottom of the "Edit Widget" screen. This will allow resizing the table horizontally and vertically.
Here's the table widget resized to allow another widget to be placed to the right of it:
Here's the table widget resized to only allow two rows to be displayed:
Please note that the columns will automatically adjust according to the size of the table. If you find that the text under the first column is being cut off, you can enable a widget setting called "Wrap Text". This will provide the column extra width to display more characters.