How to configure ram?

Ha! Found it!

Documentation

It looks like you are unable to completely disable the onboard video. My guess is that they want to charge you a C-Note for an updated BIOS which provides that option. There may be a free BIOS floating around somewhere, but flashing it always carries some risk. Personally, I think 256MB is not really worth going to extraordinary measures. For half of what they want to charge you to "fix" it you could replace your RAM with a pair of 4GB sticks and have 8GB (minus the measly 256MB for the onboard video, of course.)

With the cautionary note that Dell is famous for having dozens (or more) of possible configurations of computers bearing the same model number, I'm sure you can. The picture I found for your rig shows a total of four RAM slots. I'm guessing that only two of them are currently filled. Adding two more 2GB sticks would total 4GB more RAM for a grand total of 8GB. The only hitch here is that mixing brands and types of RAM can occasionally cause problems. The safe route is to remove the RAM that's in there and replace them with a matched set guaranteed to work with your computer.

Crucial is an outstanding brand and promises to replace anything which doesn't get along with your computer:

SDRAM, DDR2 and DDR RAM memory upgrades from Crucial.com

(For some reason, some of their recommendations are way overpriced. You can do better price-wise.)

Fortunately, RAM is dirt cheap these days, which makes the "safe route" I described above even more appealing.
EDIT: Looks like DDR2 RAM has actually gone UP. I'd consider adding a 4GB kit with a compatibility guarantee.

Here are some examples:

Newegg.com - Computer Hardware, Memory, Desktop Memory, 8GB (2 x 4GB), 240-Pin DDR2 SDRAM

Finally, I am sorry to hear about your dad. Looks like he was quite a guy who certainly lived a full and worthy life. God bless you and your family.

A couple things worth mentioning, since the impetus behind your wanting to max out your RAM is due to perceived slowness of the computer.

1) 4GB (minus a tad for the onboard video) is a respectable amount. Unless you are doing video editing or rendering, or are in the habit of having dozens of things running at once, it ought to serve for most other purposes. Without knowing what you use the computer for it's hard to say if adding loads more RAM would be a dramatic improvement.

2) Which brings us to another issue. Dell is fond of putting a lot of their utility programs on their computers and having them all load at startup. I'd recommend running Startup Inspector for Windows - Free and then use the Snipping Tool to post a screenshot of what it finds. Chances are that you have stuff running behind your back that you don't need.

3) Fill out your complete System Specs - someone with eyes sharper than mine may have some suggestions.

4) Your CPU is showing it's age a bit, it's listed as a Intel® Core™2 Duo Processor E6550 2.33 GHz. Don't expect miracles.

On the whole, if you're mainly using the computer for email and the Internet you can get by for a while. The fact that you're locked into (what I discovered yesterday) is still pricey DDR2 RAM means that I wouldn't sink a lot of money into upgrades. When the time comes, you'll get far more bang for your buck by saving the dough now and putting it into a brand new system later. I am one to use my computer until I run into something I really want to do and can't, due to the limitations of my current hardware. Unless someone is made of money it makes no sense to upgrade "just because". :)

If you download the Freeware version of SIW, it has a section that tells the maximum memory you can install on your particular MB.

Buy SIW Pro or Download SIW Freeware