So you have a leaking toilet and want to remove the tank from the bowl to fix it. However, the wing nuts on the tank bolts are so corroded, they’re stuck. Even a screwdriver in the slotted head of the bolt doesn’t provide enough leverage to break the weld between the bolt and its wing nut.
Two popular remedies are:
Cut the bolt with a hacksaw blade (a bit of effort); or
Grab the threaded part of the bolt below the wing nut with a vice grip (risk damaging the threads and making the nut even harder to remove).