Changing Base Fields?

I’m a complete and absolute novice with Base but I’ve managed to create a “Member’s Form”. When I set up the fields I made a couple of fields too short (number of characters).
Is there any way of being able to modify this or do I have to start again?
My idea was to enter about 20 members and then experiment with creating reports and queries as honestly I find the “Base Handbook” that I downloaded very, very, heavy going.
Thanks for any input

I assume that you want to alter the field sizes in a Table. You can do this in edit mode. You can increase the size but not decrease it.