Questions & Answers about Resimleri duvara düzgünce asmalısın.
The suffix -i is the accusative (definite object) marker. In Turkish, if the direct object is specific or “definite” (like “the pictures” rather than “pictures in general”), you add -i (with vowel and consonant harmony).
• resim + ler (plural) → resimler
• resimler + i (definite object) → resimleri
So Resimleri means “the pictures” as the definite thing you’re hanging.
The suffix -ce (one of -ca, -ce, -ça, -çe, chosen by vowel harmony) turns an adjective into an adverb of manner.
• düzgün (adjective: “neat, proper”)
• düzgün + -ce → düzgünce (“neatly,” “in a neat manner”)