Updating to Version 2.1.0 Question

Team,
Regarding the Update from 1.5.8a to 2.1.0, Is this handled pretty seamlessly by the site itself? I am a noob at Zen, We have a Web person who normally takes care of these things for us. They are stating that I need to Update our Site for "Security PCI Reasons" immediately at the cost of $1,500 or >. Now I am familiar with Wordpress Plugin updates etc where its pretty much Seamless.. Does Zen work the Same? Meaning... Is our person likely just going to press the Download Button and Zen will Update itself? ... And they send me a $1500 Bill? I am reluctant to simply press the button before talking to someone.. I figured I would post here to get your professional opinions.. Our site doesnt make much in revenue itself, and to pay a $1500 bill for us is difficult.. Any opinions suggestions would be appreciated.

I attached a Screenshot of the Download Button..

Thank you!

Zen Cart upgrades aren't a "push a button and it's done" process. The cost of your upgrade should depend on your current Zen Cart version as well as the number of plugins, add-ons and customizations performed for the site.

Zen Cart 1.5.8a isn't too far behind 2.1.0, but there are a number of files from 1.5.8a that are no longer used and will cause problems if not removed. $1500 isn't totally out of line, depending on the site's customizations.

Thank you for this information.. That makes perfect sense..