According to the information brochure available at: https://jkbopee.gov.in/Pdf/Downloader.ashx?nid=67&type=1, you can opt for upgradation. But you need to remember that a seat allotted in Round 2 is mandatory to be taken. Once you get a seat upgraded the seat allotted in Round 1 will be canceleld automatically. So you can join and opt for upgradation by indicating the fresh preferences for the seats to be filled up. Only those Candidates who do not join the allotted college are not eligible for Round 2 of Counselling. But if you report and join the College allotted in Round 1, you can opt for upgradation. And regarding your chances for a better seat in Round 2, you haven't mentioned your Category.Compared to 2019, the NEET 2020 cut offs have changed considerably higher than expected. With the top score being 720 which is 19 marks greater than 2019's top score, it is difficult to predict chances. But based on the analysis of the experts, on the and going by previous years data, with a score of 499, you might secure a seat in Government Dental College if you opt for upgradation.