It's best not to mix the oil spec.
If you intend to use 5W30 from now on, change the oil and filter.
This will also give you a chance to inspect the engine undertray to see if there is much oil saturation on it.
If you were just going to top up, use 5W40 until you are ready to chage the oil and filter.
Silver 2002 1.4 TDi SE
Heated Red Sports Leather 4 Seat Interior, TTS FBMFSW, Open Sky System, Bose, RNS-E with Audi Bluetooth Telephony & SDS, DIS, Audi iPod link, Cruise Control, Komfortblinker, New Style Asymmetric Key Fobs, Rear Cup Holders, 4 x Electric Windows, Auto-dimming Rearveiw Mirror, A2OC Mats, TT Pedals, Puddle Lighting, Headlight Washers, Headlight Protectors, Debadged, 0.659 5th Gear, H&R Front and Rear ARB's, Koni FSDs & Weitec -30 Springs, Rear Disc Axle Conversion, ATE Powerdisc and Ceramic Pads, 17" TT Ronal Wheels with 215/40 Tyres, Floppy Wiper, Votex Body Kit, Spacesaver, Heated Wing Mirrors, K&N, Stealthed & a Coat-Hanger!