Ios app easily crashed by IOS memory issue

I’m chinese. my english is not good. so i hope that you understand what i saied.
I Found my App which running on iphone6 can easily crashed by memeoy issue. becase iphone6 has only 1 GB Memoey.when my apps’ running memory reached half of 1GB Memory, the app killed by ios system. but the app running on iphone7, becase the iphone 7 has 2GB memory, the situation will never happen.
I found the texture memory is large. to slove this problem, i tried to scale image small in memory before load it. but the crash can happen also.
what i should do to reduce app’s running memory(texture memory、code memory…).
I hope you can help me. I thank you very much!