@pelo
Before you update to WooCommerce version 3.0 or greater, you just need to make sure you have the latest version of WC Vendors (right now it is v1.9.11) and WC Vendors Pro’s latest version (v1.4.3)
Those are now compatible with WooCommerce 3.0++ . WooCommerce made many changes for version 3.0, so we had to make some changes in our plugins as well to remain compatible. Older versions (older then 1.9.9 free and 1.4.0 Pro) of WC Vendors and WC Vendors Pro will not work properly with the new WooCommerce.
If you already have WC Vendors v1.9.11 and WC Vendors Pro v1.4.3 installed, then you do not need to remove them before updating to WooCommerce 3.0++