To change the default size and anchor-point of all new text, use the "Text" preferences (in menu File / Preferences..., "Display" section, "Text" tab). The top part of the dialog controls how new text will appear. Select the type of text, and then its appearance (size, anchor-point, font, style, etc.)

Below the "Default Text Style" is a section that controls the fonts used to display textual cells.

Below that are controls for "smart placement" of text, which adjusts the grab point according to the environment of the text. This currently applies only to export names, which are placed relative to the arc connecting to the exported node. For example, if a node on the left end of a wire has an export, and the "Horizontal" placement is set to "Inside", then the export text will attach on the left side, causing the label to appear inside of the wire.

The bottom part of the dialog controls text drawn in circuitry. You can choose the font to use, as well as a global text scale. Normally, all text is drawn at 100% of its stated size. However, you can globally scale all text by typing a value other than 100 into this field. You can also use the Increase All Text Size and Decrease All Text Size commands (in menu Edit / Text) to change this value, and alter the size of all displayed text.