You need to find out what exact panel you currently have, you can try googling and i think hwinfo64 shows exact panel model. Then you should look for what dimensions and connector your panel has, you can find this info on panelook.com. laptops made in the last 10 years mostly used edp connectors, there are a few different ones that are not compatible with eachother.
Panels with resolution that is 1920x1080 or lower use a 30 pin connector, Touch panels use a 40pin connector. Higher resolution panels (2560x1440, 4K) also use a 40pin that looks the same but is NOT compatible with the touch 40pin. Newer laptops and panels sometimes have a connector with 0.4mm pin pitch which is not compatible with the normal 0.5mm pitch connectors.
If your laptop was sold with a high res panel option you can find a 40pin cable for it, But as the motherboard side of the cable is non standard if your laptop only came with lower res panel options you will have to stick to 1920x1080 panels that have the 30pin connector.
Look for panels on panelook that have a compatible connector and have the same or a bit smaller outline dimensions than your current panel. Once you find a good panel you can look for it on ebay and aliexpress, You should message the seller to make sure that you are getting the exact panel as often they will send whatever compatible panel they have in stock that can be a lot worse.
The panel you get may just be a drop in replacement or you may need to modify the lid as even if the outline dimensions are smaller the pcb at the bottom may be wider or the connector in a sligthly different place.
There are still a few possible issues that you can run in to, Some laptops have a panel whitelist or are designed in a way that makes panel swaps hard or impossible, you should try to find out if anyone has done a panel swap to your laptop before.
While the additional pixel density does not provide much benefit, and infact is pretty bad for battery life. There are other reasons to go for a 4K panel, 4K panels are usually much better than FHD ones, For example the panel i chose has much better brightness (600nit vs 250nit), contrast (1200:1 vs 700:1) and color gamut (74% vs 34% rec 2020) than the stock FHD panel in the T480. But while not as plentiful you can find very good FHD or 2560x1440 panels aswell. So why did i go for 4K then? Because its a lot more fun! And unlike a FHD or 2560x1440 T480, You cant exactly go and buy a 4K T480 anywhere, You have to mod it yourself.