Can I update to OS X El Capitan on my Mac bought in 2014?

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.

Does the >>  Computer Qualify for the Monterey upgrade 

macOS Big Sur 11 hardware requirements

macOS Catalina 10.15 hardware requirements

macOS Mojave 10.14 hardware requirements

macOS High Sierra 10.13 hardware requirements

macOS Sierra 10.12 hardware requirements

Caution - jumping over all the newer versions and directly to Big Sur  / Monterey on Qualifying computers is Technically possible - there are those who have attempted and were successful. Then there are those who attempted and had less than good results.

If this is a Production or Mission Critical Set-up - a more prudent and measure approach is suggested. 

The above is from observations on the Apple Support Community Forums and IMHO

Tips Big Sir Upgrade Released Nov 2020

Tips Monterey Upgrade  Released Oct 25, 2021

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

Notation - Mojave is the Last version to support 32 bit applications / extensions and Drivers. Catalina, Big Sur & Monterey supports only 64 bit and there is no workaround.

Suggest using Go64 to find 32 bit application before attempting the upGrade. Some or many of the Application already installed may required update or upGrades to 64 Bit Versions.

Are there any AntiVirus, Disk Cleaner, Optimizers, Un-installers, etc installed which should be removed as per Developers Instructions. They are useless, unneeded, cause havoc and interfere with the normal  operation of the OS and may even Corrupt the OS requiring a Reinstallation

Back up your data, check your applications for compatibility, and depending on which Mac model you have, click on High Sierra, Mojave, Catalina, Big Sur, or Monterey. If you're trying to upgrade to El Capitan, yes.

Catalina and newer won't run 32-bit software; download and use Go64 to scan for it. To check other programs, click here and look them up.

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It is NOT worth the effort to upgrade your older Mac - you will continue to run into multiple problems with outdated browsers, too.

2014 Macs are pretty much obsolete.

You really should be buying a newer Mac.

You can always migrate the data files to a new system.

I have a 2014 Mac laptop and an iMac myself, that still are still running on El Capitan (10.11). I'm impressed that these computers still work so well after 7 years. However, I have more and more problems going to web sites from them and of course, there are no more updates I can apply to the applications they have.

Disagree and the computer is capable to upgrade to something more recent. It just needs to be done with due dlilence and good planning.

Yes, 2014 computer are not the most recent but usable depending on the Uses needs.