At the top of your screen there is usually a button called 'View'.

Click on this and go to either 'Text size' or 'Text zoom'

If you have 'Text size' click on this again, and you will have a choice of sizes so that you can enlarge the size of the writing on all the pages you look at.

If you have 'Text zoom' click on this again, and it will allow you to enlarge or decrease as you wish so that you can enlarge the size of the writing on all the pages you look at.

You can put it back to normal again at any time by going through the same process.