well now its the 9 time i got such a q by email this month and i decided that its time for some one to post a step by step guide thru 
ok we are gonna make the den of evil lead to catacombs 4
for this we need one file: Levels.txt first take some paper to write some stuff down it will help you later
ok in the first col u will see the areas Cave 1 and Catacombs 4, write down the ID numbers for those areas which are 8 and 37 also write down the row number it will help later as well which is 10 and 39
now goto the columns vis0-vis7, which stand for visit or something these are actually the "doors" towards other levels (the warp0-7 columns are not directly related so ignore them now editing those is not needed so leave them alone)
now you will see that the den of evil row has its first vis0 set to 2 which is the ID of the Bloodmoor change this to 38 (catacombs 3) (note this is important since if you have a door that leads to 2 locations u will crash!) now goto row 38 which is catacombs 3 and change the warp entry set to 39 into 10 so that it leads to den of evil now to the actuall remap, goto row 4 (bloodmoor) and change ALL the entrys that say 10 into 39, now go to row 39 and change the entry that says 38 into 2 so it leads up to the bloodmoor if you did it all right now enter the game and go to the den of evil when u enter the cave u find yourself in catacombs 4 (NOTE all areas seam to work except the treasurecaves for some reason)