Updating an esp, assuming it's an esp that needs to be updated and not some other type of file, is very easy. You'll need Creation Kit, and for that, you'll need to download the Bethesda Launcher: https://bethesda.net/en/game/bethesda-launcher and install it. Then, from the Bethesda Launcher, install Creation Kit. Put the esp you want to update in the game's Data folder, then click the CreationKit.exe in the game's install folder to open Creation Kit. In Creation Kit, click File > Data. Select the esp you want to update. On the right of the screen, you'll see a list of the esp's master files under "Parent Masters." This will tell you which master files you need to load along with your esp. Double-click the master files you need to load to place a checkmark next to them. Select your esp and place a checkmark next to it if it hasn't already been checked. With your esp highlighted, click "set as active file" then click "OK." You'll get a ton of error popups as your esp loads. Just click "Yes to All" every time an error message pops up. I don't know what those errors are for but everything I've read says just to ignore them. So, I've always ignored them. Never had a problem an updated esp. Depending on the esp, Creation Kit can take forever to load. After it loads, there will be a new little window that pops up that lists all the errors. Close that window. Then save your esp by clicking the save icon at the top. It looks like a floppy disk. And that's it! Close Creation Kit and replace your old esp with your new esp.