Why is space too tight for a USB WiFi+BT adapter? That would be the easiest solution. The Dell WiFi+BT card is probably a mini-PCI-e card. So you'd have to disconnect the antenna cables and then remove the card from the mini-slot if you get a WiFi 6 + BT 802.11ax mini-card, but choice and speeds may be more limited. Make sure the card supports your version of Windows. You have two PCI-e x1 slots on the motherboard so a x1 WiFi+BT 802.11ax card could work. Again, make sure the card supports your version of Windows. You'll still want to remove the mini-card and figure out how to connect the antenna wires to the new card, assuming they can reach a card in the x1 slot. You will also need a dual-band router/modem that supports 802.11ax to get WiFi 6 support. If your accessories (eg, keyboard, mouse etc) don't support BT 5, make sure whatever card you get is backward compatible with the BT version(s) your hardware supports.
Will this motherboard take a PCI-e upgrade card to wifi 6 + bluetooth 5.2 (or 5.0)? Speccy says -  Manufacturer Dell Inc.Model 088DT1 (CPU 1)Version A00Chipset Vendor Intel I have two spare PCIe slots and the mini PCIe port that the current wifi and bluetooth is plugged into - I don't want a USB dongle as space is tight! So internal is the way to go. I have the original DW 1705 in there (2.4 only). Any suggestions that won't break the bank?
Inspiron 3847 wifi + bluetooth upgrade