Suggestions are:
1.) a pipe wrench on the old hose connection
2.) water pump pliers on the old hose connection
3.) WD-40 sprayed on the old connection at the thread area to loosen the corrosion gunk.
4.) or Coca Cola dribbled on instead of the WD-40 but for the same reason.
For Suggestions 3 and 4 let the Coke or WD-40 work for a while before using Suggestion 1 or 2.