For finding left over code, you'll probably want to hire a developer, if you aren't familiar with coding.
One thing I found on the front end is that you might want to remove links to buddha-crosssell-db.js from your code as that is resulting in a 404 error.
There's also an error in your theme.js file you might want to look at/ hire someone to look at.
As for improvements, they're pretty much the standards for most shopify themes:
Make resources non render blocking
Preload hero image
Remove lazyloading from hero image
Preconnect to critical origins
They're are multiple versions of jquery being loaded (3)
Remove src link from lazyloaded images, leaving only data-src
Optimize images with a compression app
Consider deferring the loading of your tidio chat app to scroll.
I ran your site through our team's Shopify Analyzer, a free tool that we built for the Shopify community.
You can view your report at this link: https://analyze.speedboostr.com/result/fw6qbi8mat
It'll give you some insights into what can be done to improve website performance.
Overall, it looks like your website could benefit from the following:
If you need any help with the above, please don't hesitate to reach out!
Here is our brief analysis of your store:
Scripts make your performance indicators worse, take a look here: https://prnt.sc/1065t0a and https://prnt.sc/1065os2 there are too much of them. Around 225 and the weight of them is around 2.3 MB which also a lot. A lot of pictures without Lazyload applied as well: https://prnt.sc/1066kb1
Total at the moment, the indicators for each page you have: Home - 18, Collection page - 39, Product page - 19
Hope that helps you. Take a look at our article, your case is similar to our example here: https://speedimize.io/blog/speed-store-improvement
If you will have any questions, we will be glad to give our advice on how to make your shop faster.
By the way, take a look at our simple explanation on how to optimize your PageSpeed metrics here: https://speedimize.io/uploads/pagespeed_speeddimize.pdf
Looks like the link above expired, here's an updated one https://analyze.speedboostr.com/result/fw759u893m
Looking forward to your reply.