You can do this a few different ways - including on the Universe, on the ETF screen or going via 'Edit portfolio'.
On the Universe page (Portfolio>'+Add Securities'), you will find a delete button (grey bin) next to the 0% ETFs. Please see the screenshot below:
When you open a zero value/weighting ETF in your Portfolio you will see a "Remove from portfolio" button (Blue text with a blue bin icon at the end) on the right-hand side, below the ETF Price. Please see the screenshot below:
Alternatively, click on the ‘Options’ button on your dashboard and select ‘Edit portfolio’, which takes you to a screen headed ‘Set portfolio weights’
To remove ETFs with a zero value or weight, click on the bin icon next to that ETF.
Additionally, you can adjust target weights for the ETFs in your portfolio from here.