I am not able update OS in my macbook pro

braja240 wrote:

I am not able to update os in my macbook pro.In system preference i am not getting option for software update.

Well you do not state what Mac, what macOS you are currently running and what you expect to update to...(?)

Does your Mac support an update OS... Verify your tech specs if in doubt.

Big Sur macOS 11.4

https://support.apple.com/macos

older macOS installer backups on this server:

https://support.apple.com/en-gb/HT211683

verify you are using the Safari browser to download/initiate the macOS links.

For us to effectively answer OS update questions, we need more information from you:

1) Your MacBook Pro's sub-model.

2) Its current macOS version

Both are easily available by doing "About this Mac..." form your Apple menu to get a screen similar to this:

The ability to upgrade and how to do it depends on both those important pieces of information. Older MacBook Pros cannot run the latest macOS versions.