I was experimenting with using update manager to upgrade a 3.5u4 host to V4 and pointed the update manager baseline to upload the iso to a datastore that the 3.5 node could not see ( boy do I need more coffee...).
I thought I could delete the baseline and start over but every new baseline does not give me the option to choose a datastore to upload to. I have looked in the database tables but do not see a record to modify.
if you start new upgrade remediation you definitely should have an option to select storage for upgrade. It could be ESX local or network(SAN) datastore that the ESX console will be put.
It is not necessary to delete the baseline, but if you did this you can create a new baseline - no need to upload a new .iso file you can just select it from the dropdown list of the New Baseline Wizard. When you delete the baseline its iso file is not deleted - it stays by default in C:\Documents and Settings\All Users\Application Data\VMware\VMware Update Manager\Data and can be selected when you create another baseline.