Micro. works word processor! Every time I need to chage a word or letter the next word gets deleted.?

I write short stories and when I need to change a sentence, phrase, dialog etc. The letter next to them deletes to where I cant even hit the space bar without losing a letter or word. I get stuck retyping the whole paragraph. There has got to be a way to turn that stupid action off. Please help. I'm no computer guy so this is abig problem for me and my work is suffering. Thank you.