You have to create a plot style with the desired text height and assign it to your view.

Here is a step by step guide that might help you.

• In the design, tab choose plot styles and add a new plot style (lets name it plst01)
• In the design, tab choose plots and add a new plot
• Select the New plot and choose Edit
• Right click on the paper and insert a view
• With the view on the paper selected, go to properties menu and select the plot style you created found under Appearance->Plot Style->click on the empty cell and select plst01 from the drop-down list
• With your plot view window open, go back to your plot style and choose the desired text size found under plot style's Properties->Dimensions->Text size. Your size changes will automatically appear in your plot.