If you are having troubles reading the messages in Skype you can easily change the text size to suit your needs.

Here is how you can do it:

1-Once you signed it, go to tools / options

2-From there, click on IM&SMS, and then IM appearance

3-You will see the option for changing the font.

4-When you click it, you will see a regular font selection option, where you can choose font, font style and its size.