Can I change the margins in pages?

Using Pages for MacOS, yes. Open your document, then click the Document button at th right end of the tool bar to open this sidebar window:

Default margins are 1" on all four edges, Those widths will be posted in inches or centimetres, depending on the Region setting of your computer.

Using Pages for iPhoneOS:

Please note: I am NOT familiar with Pages for iPhone, including the sections mentioned in the list below.

The descriptions are notes on a first time going through the process and recording the steps.

The notes may be incomplete and may contain some errors in observation or in reporting.

Regards,

Barry

Open the Template screen.

Tap the template you want to use for your document.

A set of related templates will appear in the bottom half of the screen.

Choose one and tap to open,

Tap the format brush to open that specific template, and present the top portion of a format menu in the bottom psrt of the screen.

Scroll down the menu list, and tap Edit Pages Template.

This will open a page similar to the Document format pane in Pages for MacOS, where you can change the margin settings and other format items that apply to the whole document.

On an iPhone tap the 3 dots, tap Document Options then Document Set Up, then More Options and drag the margins.

On an iPad, instead of tapping the 3 dots, tap the document's name and proceed as above.

Thanks for chiming in, picas!

As noted above, I'm not familiar with Pages on the iPhone (or on iPad). Happy to hear from someone who is!

Regards,

Barry