A method for replacing a first sheath, whose distal end is positioned inside a vessel and whose proximal end is positioned outside the skin of a patient, with a second sheath may involve inserting a dilator over a guidewire and into the first sheath until a distal end of the dilator and a distal end of the guidewire are positioned inside the vessel. The dilator may be hubless or include a removable hub, and may define an external channel configured to receive a second guidewire. The method may further involve removing the first sheath, thereby leaving the dilator and the guidewire in place. After removing the first sheath, a second sheath may be passed over the dilator and the guidewire until the distal end of the second sheath is positioned inside the vessel. The method may further involve removing the dilator and the guidewire, leaving the second sheath in place.