i need help on how to upgrade to a higher version from OSX Yosemite 10.10.5 to a higher version.Can someone kindly help here?

First of al there is no Apple Support Team here, this is a users to users community, Apple do not take part.

Secondly in my first post I gave you all the information you need to discover what year your mac is and by

using the links provided you would be able to ascertain that your 2011 mac can only upgrade as far as

macOS High Sierra the information is there on how to obtain the upgrade as well.

macOS High Sierra can run both 32bit and 64bit apps.

Open Safari, do not use Firefox.

Click on the How To Get old versions of mac OS's link in my first post,

scroll down to Download OS and click on macOS High Sierra.

This will redirect you to the App Store High Sierra download page,

it should say Get or Download.

Again follow the instructions in my first post about backing up and

checking your apps in Roaring Apps.

The App Store Updates page only informs you of updates available for the OS you are running.

Installing a newer OS is called an upgrade.

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 older OS’s,

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.