How can I upgrade to a newer OS from High Sierra?

Yes your 2011 cannot upgrade any further.

Have you ever downloaded Pages before if so go to the App Store Purchased

section and click on Pages it should download the version compatible with High Sierra.

If not you can have a look at the free app Libre Office, https://www.libreoffice.org

Which OS you can upgrade to will be governed by which model and year your mac is.

Click on the  top left of your screen click on About This Mac to find out the year of your mac.

For Mojave or Catalina,

Open Safari and click on this link, 

How to get old versions of macOS – Apple Support

Go to Check Compatibility to see if your mac qualifies for the OS upgrade you want.

Then go to the Download OS section and click on the OS you want to install.

If you want to or are able to install Big Sur, open Safari and click on the link below.

How to upgrade to macOS Big Sur - Apple Support

Before upgrading make a full back up of your Mac.

Check that third party apps you use have updates available for the new OS.

https://roaringapps.com

Check that your printers/ scanners etc have updated drivers and software available for the new OS.

Connect your mac to your router via cable rather than rely on WiFi.

Do not use your mac while it is downloading

and do not use any other devices that share the same internet connection.

If the App Store says ‘Open’ then it is detecting a previous download of the install app

go to the Applications folder locate Install macOS ******.app.

Move it to the Trash, empty the Trash.

Restart, click on the link again, the App Store should say ‘Get' or 'Download'.

If you are considering upgrading to Catalina or Big Sur be warned they do not support 32bit apps.

Your Mac is probably running 32bit apps and these will need to be updated to 64bit apps,

some updates may be free, some may be paid. Use this app to discover which apps you have

are 32bit, https://www.stclairsoft.com/Go64/ then contact the developers of the software to see

if they are providing 64bit updates or alternatives.

Welcome, joejcl2, to Apple Support Communities!

How far any particular Mac can be upgraded all depends upon the particulars of the Mac: Model and Sub-Model.

It happens to all of us, eventually, on our older systems, joejcl2.

I have a mid 2010 MacBook that, likewise, cannot go beyond High Sierra.

However, it still serves well, for the older software that can run on it (older Microsoft Office, older Numbers, Pages, etc.).

Libre Office is an alternative to Word, very much like it and can read Word documents.

Microsoft no longer supports their apps on older macOS's.

You may well find older versions of the apps you want on unofficial download sites.

joejcl2 wrote:

I can't get MS Word for mine--or at least I can't find where to get it. The newest version cannot be downloaded on my computer.

Admittedly, I obtained mine “back in the day”. (Back while High Sierra was the latest.)

Look into the Free LibreOffice, it handles MS Office files like Word & Excel…

https://www.libreoffice.org/

Oh I'm surprised I never mentioned Libre Office,

wait a minute I did, twice.

Sorry, didn't read every post. I see now you did! :)

Oh you should always read every post you never know what people are saying about you.