How to change the title font size?

To change the title font size, go to the block Settings → Typography → Title: Font size. Specify the value you need, save the changes, and publish the page.

If this is a block with cards that have a title, then title font settings will be applied to the cards' titles. To change the title font size for the whole block, select the title, in the context menu that appears, click on the "Text size", and select a suitable value from the list.

You can delete the title from the current block as well, add a block from the "Title" category above it, and specify its font size in the block Settings. You can set the blocks' paddings in the blocks' settings. Save the changes and publish the page.