"It is much bigger."
Translation:Tá sé i bhfad níos mó.
"more" is usually a determiner or an adverb, while "bigger" is an adjective. Adjectives typically follow the noun in Irish. So Tá níos nó madraí ná cait ann means "there are more dogs than cats", but Tá madraí níos mó ná cait means "dogs are bigger than cats".
In many cases "more" and "bigger" are basically interchangeable in English - "we need more staff"/"we need a bigger staff", "I want a bigger breakfast"/"I want more breakfast" but the adverb/adjective distinction still applies.