Is that possible to switch an Open Source Project license from GPL to LGPL v3 ?
I am the project originator and the only contributor.
AFAIK, you can do that if you're the only contributor to the source code, irrespective of whether you're the original author or lead developer.
If you can get approval from all the contributors, then you can change the license.
Warning: IANAL.
yes, of course. You can change the licence to whatever you want.
Go to your admin page, then edit registration from the menu, view Public Info, then edit the Trove categorisation. You need to remove then add a new category. Easy (if a little link-happy).
This applies if you're an admin of the project, no matter how many of you there are or who has contributed.
In addition to the points noted, note that anyone to whom the product was already licensed (and anyone they licensed it on to) would be entitled to stay under the GPL - you can't change the terms they took the software under (unless they agree to the change).