If I use a pre made logo from Envato Elements, like this one: Boar mascot, Graphic Templates - Envato Elements, but change certain colours and fonts etc, can I still use this logo for website, on tee shirts etc?
You can use it on website but on t-shirts depends:
If it’s gonna be a free t-shirt for the company employees, you may.
If you’re going to sell the t-shirts or another items, you cannot.