In general, increasing the size of the DIMMs installed typically does not increase the power load or thermals -- but it does if you increase the number of DIMMs. For this specific case, online specs tell me that (a) you are limited to two DIMMs (so typically no power or thermal issues) and (b) upgrading to 4GB of memory *is* supported. I would thus conclude that you should be able to go ahead without issue. Now, remember that this is just my (albeit educated) opinion; you really should be verifying this with Dell (after all, it's their system design, their motherboard design and their BIOS implementation).
If your purpose behind this upgrade is to make the move up to Windows 10, understand that neither Intel nor Microsoft formally support the use of Windows 10 on systems this old. This does not mean that Windows 10 will run; it simply means that,
- Intel does not provide device drivers to support hardware this old. Microsoft does provide compatibility drivers, but performance and feature set may be curtailed using these drivers (this is especially true if you are using the chipset-based graphics engine).
- If there is a problem with the compatibility drivers, Microsoft will not help you. Their stance is that these drivers are provided as-is.
Hope this helps with your decision-making,