Be certain to work on the system when it is completely cool, not warm at all. I suggest letting it cool overnight; otherwise, you may get burned.

A closed end wrench through the upper hose connection and then over the fitting with an upward pressure should compress the fitting enough to remove it without breaking anything. If you slide a closed end wrench (8 mm? IIRC) over the new fitting before installing it you will see how it compresses the fitting to allow removal of the old one.

The radiator necks are fragile, be gentle with the hose removal/installation so that it does not break.

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