Can I upgrade my iMac to macOS Ventura

What model year is your iMac? The model year of an iMac is available at Apple menu > About This Mac.

An early 2009 iMac can be upgraded to El Capitan 10.11.6 but no later version 

A late 2009 through mid 2011 iMac can be upgraded to High Sierra 10.13.6 but no later version. 

A late 2012 through late 2013 iMac can be upgraded to Catalina 10.15.7 but no later. 

A mid 2014 and late 2014 iMac can be upgraded to the latest version of Big Sur macOS 11 but no later. 

A late 2015 or mid 2015 iMac can be upgraded to the latest version of Monterey macOS 12 but no later. 

A 2017 iMac can be upgraded to the latest version of Ventura macOS 13 but no later. 

For all of the above, see instructions in: How to download and install macOS - Apple Support

  A 2019 or later iMac can be upgraded to the current version of Sonoma macOS 14. See: How to upgrade to macOS Sonoma - Apple Support

If compatible with your iMac: Upgrading from MacOS 10.11 (32 bit appa) to Ventura (64 bit apps) would have to be done very carefully, and in gradual steps through the upgrade versions.

Apple support's article: macOS Ventura is compatible with these computers - Apple Support

says:

• iMac (24-inch, M1, 2021)
• iMac (Retina 5K, 27-inch, 2020)
• iMac (Retina 5K, 27-inch, 2019)
• iMac (Retina 4K, 21.5-inch, 2019)
• iMac (Retina 5K, 27-inch, 2017)
• iMac (Retina 4K, 21.5-inch, 2017)
• iMac (21.5-inch, 2017)

As we do not know which Mac model (year) you have, you may want to identify your iMac in those listed in the article below ... also: underneath that model's illustration, you can read the latest MacOS version that is compatible with that model:

See how to: Identify your iMac - Apple Support

ie: Any model that says MacOS Ventura or MacOS Sonoma is the latest compatible version iwould be able to be gradually updated to MacOS Ventura, providing the transition between 32 bit apps and 64 bit apps is carefully handled.

About the transition to 64-bit technology and how it affects 32-bit apps:

32-bit app compatibility with macOS High Sierra 10.13.4 and later - Apple Support

Update: Ooops thought I was replying to an unanswered question ... apologies all round 🤗