Anyway I can change the font size on the watch? I wear glasses only to read so any notification showing on the watch or simply navigating the watch I struggle to read the watch face.
You can choose a watch face that's easier to view: either one of the built-in ones, or downloaded from the Garmin web store. See p13 of the PDF manual.
For the built-in ones there's not a lot of choice:
Watch Face Settings
You can customize the appearance of the watch face by selecting the layout and accent color. You can also download custom watch faces from the Connect IQ store.
Customizing the Watch Face
You can customize the watch face information and appearance. 1 From the watch face, hold UP.
2 Select Watch Face.
3 Select UP or DOWN to preview the watch face options.
5 Select Accent Color to change the accent color (optional).
There's a better choice in the online store: https://apps.garmin.com/en-US/devices/forerunner45/apps?sortType=mostPopular. You'll have to experiment, but I found a couple of "large print" faces that suit my fading eyesight.