Ajax Cart for WooCommerce makes buying smoother in two ways:

On the classic cart page (the [woocommerce_cart] shortcode most stores and classic themes use), totals are recalculated with AJAX as soon as a quantity changes — no “Update cart” click — with -/+ buttons around the quantity.
A side cart (optional): a cart drawer that slides in from the side — or a popup — when a product is added, with a floating cart button, a coupon form and a free shipping progress bar — on classic and block themes alike, on every page but the cart and checkout.

On the newer Cart block (the default for stores created since WooCommerce 8.3), WooCommerce already updates quantities by itself; there the plugin adds a confirmation before an item is removed, and the side cart works the same.

No other hacks, code or theme changes are needed: the features are active as soon as the plugin is.

You can try and play with this plugin demonstration clicking here

Free version features:

Automatically reload and recalculate the classic Cart using AJAX when quantity changes
Show -/+ buttons around item quantity on cart page
Show item quantity as select instead numeric field
Show user confirmation when change item quantity to zero — and, on the Cart block, before an item is removed
Side cart: a cart drawer that slides in when a product is added — or a popup in the middle of the screen — with a floating cart button and item count
Coupon form inside the side cart: apply or remove a coupon without leaving the page, the totals and WooCommerce’s messages right there
Your own look for the side cart: accent colour, the floating button’s icon and corner, and its texts (title, checkout button, empty cart)
Free shipping progress bar (“Spend $12.00 more for free shipping”) in the side cart, Mini-Cart, classic Cart and Cart block — the amount read from your free shipping method, or your own

Premium version features:

Allow to change/synchronize quantities in shop, minicart and single product pages view demo
Make the Add to cart button to perform with AJAX, without full page reload view demo
Faster AJAX reload call when change quantities in Cart page
Option to lock quantity inputs to allow only change using plus and minus buttons
Update price vs quantity calculation automatically on Single Product pages (view demo)
Change quantities with -/+ buttons inside the side cart (view demo)
Undo a removed item on the Cart block (view demo)
Minimum, maximum and step for every product quantity, on the classic and the block cart
Rewards progress bar: your milestones on the way to bigger orders (“$50: free gift”, “$100: 10% off”) in the side cart, Mini-Cart, classic Cart and Cart block — it shows the progress, the rewards are your own coupons or rules (view demo)
Product suggestions in the side cart: the cart items’ cross-sells (or upsells), each with an AJAX “Add” button (view demo)

Get the PRO version here.

If you looking for a related plugin with more complete features maybe you can try Better Usability for WooCommerce plugin.