how do I know if I have ios ? My phone is version 4 Iphone

I have had my phone about 2-4 years, I am totally frustrated because I do not know how to update. there is always another step before I can do the update, now it says I don't have enough space, they want you to buy apps and then they want me to take them off so an update can be done? Also the apps constanly need updating, is this normal? I am 68years old and my children get frustrated with me because I do not know how to do what they do on the phone. I have learned to take notes on one sheet, but I do not make individual notes because I am not sure I will find them, for me the note is a list I can refer to. I have learned to add phone numbers, but not automatically when someone calls. I also can not figure out how to send a text to a person instead of calling. if they send me a text I just reply, but I have a granddaughter who likes texting better, and I would like some help on how to resolve these issues because I need some brownie points with my family and I think I am not getting calls on my phone as a result of this problem. I have tried 3 times to update.

I do not know which operating system I have