Hi Nick, and welcome to the forums! RAM is often a deciding factor on older computers, but 4 GB should be enough for you to run any distro that you would like. If you are new to Linux, some of the most often recommended distros are Linux Mint, Linux Lite, Ubuntu, Zorin OS, and more. These are all from the Ubuntu/Debian family, but there are other families too, such as Red Hat and Arch which each have many derivatives of their own. And there are even more besides.
DistroWatch has a "Top 100" list that is a good starting point to look around and where you'll find the most common distros.
I'm pretty sure that your Dell is old enough that it has a "legacy BIOS" instead of the newer UEFI firmware. This is helpful too so that you can probably install anything. Some distros are not yet ready for UEFI.
Are you planning to install Linux only? Or do you want to dual-boot with Windows? Dual-booting is a bit easier with the legacy BIOS systems too, but still needs care during the install or Windows could be broken. A full Linux-only install is quick and easy, probably finished in about a half-hour.
Since your laptop has a DVD drive, a good way to go forward is to download a few distros that interest you and burn them to DVD. You have to use the "burn image" feature on your DVD burning software to burn the Linux .iso files so that the DVD's will be bootable. With 2 or 3 (or more) to start out, you can boot on each DVD and run that distro in "live mode" so that you get a pretty reasonable test drive of what it will be like, and you can determine if it detects and uses your system hardware like sound and wireless. Running on DVD is slower than a full install... much slower. But it's a great way to take a peek without making any permanent changes to your hard drive.
Let us know if you have any questions and we'll be glad to try to help you along.
Cheers