I want to make a text doc easier bigger so it is easier to read
Your question is ambiguous and, more, answer depends on how you use LO.
I’ll suppose you’re interested in text documents produced by Writer and similar solutions exist for spreadsheets in Calc.
Page size
If you need to reformat your document from, say, A4 to A3 (but you can also shrink from A4 to A5), change both paper size in the printer settings and the page style(s). In case you don’t bother with page styles and write in the default one, open Format → Page and go to the Page tab.
Note this only changes the paper size and your text keeps the same glyph size as before.
Text character size
If your text is fully styled, just change the font size in the root styles and you’re done.
From the ambiguity and brevity of your question, I assume you never heard of styles. Provided you did not play with font size (i.e. you did not manually change “locally” font size with the buttons or menus, which is called direct formatting), you can change everything in a single operation.
Display the style side panel with F11. Click on the leftmost icon in the toolbar if it is not already highlighted. Right-click on Default Style and choose Modify. Go to the Font tab and set a size to your liking. Click OK.
If you played with the font sizes in your text, the affected runs of characters will keep the manually modified size. Either apply manually new sizes, or if you don’t mind, select the whole text with Ctrl+A and clear direct formatting Ctrl+M. This removes all manual attribute changes, i.e. not only size, but also italic, bold, font, etc.
What precedes modifies the document and persist if you save it. If your concern is only the ability to read the document on-screen, you can magnify the display with OS utilities. You may have a software magnifying glass which offers a zoomed view under the mouse cursor. Otherwise, here are two “dirty” workarounds:
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Change your screen resolution
Choosing a lower resolution will effectively magnify the display, though the pixels being bigger, shapes will become shaggy.
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Ask your display driver to make the image bigger: your screen will only display part of the large size desktop
For example, under Linux/KDE with the nouveau driver (for nVidia cards), hitting
Window++enlarges the display andWindow+-reverts it.
If this answer helped you, please accept it by clicking the check mark to the left and, karma permitting, upvote it. If this is what you expected, close the question, that will help other people with the same question.
There’s a Zoom control on the right part of status bar, and View-Zoom menu, to avoid changing display resolution (it’s just for that: to magnify without reformatting).
@mikekaganski: thanks for reminding me this control I use everyday. When you’re busy, obvious things are easily overlooked 
Is this about printing?
As long as you didn’t set font sizes by hard formatting, but exclusively by using named paragraph styles, this is extremely simple: Look for ‘Styles and Formatting’ (Sidebar / F11) select ‘Paragraph Styles’ from the icons (supposed to be selected anyway), and pick the ‘Default Style’ from the list. This is the base style many others inherit from. If you ‘Modify’ it to a larger font size you will see all the styles that inherit from ‘Default Style’ adapting on the basis of their relative font size.
Additional base styles (not inheriting font size from Default on their behalf) are ‘Caption’‚Table, ‘Table Contents’ and ‘Text’. I do not know all the details about their relations. If you use these style or styles that inherit from them you need to manually adapt the size, too. Embedded ‘Math’ objects have their own base size.
@ajlittoz: Sorry. Was distracted for half an hour. Thus posts crossed.
@mikekaganski: I assumed the OQ knew about the zoom and wanted to get scaled-up printing.