Upgrading a late 2009 iMac

The latest compatible version of macOS is 10.13 High Sierra which you can get from the App Store or by using this link:

https://itunes.apple.com/us/app/macos-high-sierra/id1246284741?ls=1&mt=12

Apple's guide for upgrading to High Sierra:

https://support.apple.com/en-us/HT208969

Optional install method by creating a bootable macOS USB installer:

https://support.apple.com/en-us/HT201372

iPhoto will be replaced by Photos by the new OS. Mail is part of macOS and will be upgraded automatically. Apps such as Pages, Numbers, KeyNote, etc. can be installed from the App Store and I believe they are now free.

Before upgrading macOS make sure to have good verified working backups in case something goes wrong with the upgrade and the computer cannot boot or your data becomes inaccessible. You should always have backups, but they are even more important when performing such a huge system change. Don't be surprised if you find out your iMac's hard drive is failing during the upgrade or that your system needs more memory to run well.

To check the health of the hard drive run DriveDX. If the drive is shown as healthy, you can post the report here using the "Additional Text" icon which looks like a piece of paper.

High Sierra is the latest macOS that a Late 2009 iMac can run.

To get High Sierra, follow the steps at > How to upgrade to macOS High Sierra - Apple Support

Do you already have Pages on your Mac, if so open the Mac App Store and run updates. If you don't get it updated, then click on the Purchased tab (remember to log in with your Apple ID and then download Pages from the Purchased tab.

I also got updated my iMac to High sierra, but i cannot download pages(it asking for 10.14 os) and also cannot connect my iPhone to iTunes? please advise.