I have a mac book pro early 2011 os x el capitan version 10.11.6 what version if any can i update to?

The Age of this computer will Govern what newer version of macOS it will Qualify to install. Use About this Mac from the Apple Icon on Desktop - the required Information will be there.

With the above information in-hand - follow this How to get old versions of macOS and verify what version this computer Qualifies to install.  For Best results use Safari to commence the download as Others may not work.

Safari will open a redirect and open the Apple Store where the download can commence.

macOS High Sierra 10.13 hardware requirements Pretty sure this is the Last Version this computer Qualifies to run

macOS Sierra 10.12 hardware requirements

Make Time Machine Backup  is very useful and can be used to Revert to Previous Working macOS

Hi,

That can be upgraded to High Sierra 10.13.6. How to get old versions of macOS - Apple Support