Unclear Pattern Instructions

I am knitting a sweater for my 9month grandson.I am now on the sleeves.There are instructions for plain and lace pattern sweater.Iam doing the plain pattern.Using 3 needles cast on 37sts and work 12rows in rib. Change to 4mm needles.The next 2rows are for the lace pattern. These 2 rows form st st at either side of Lace Panel.Keeping continuity of 12rows of Lace Panel correct throughout inc 1st at each end of next and every foll 4th row until ther are 51 sts then every foll 6th row until there are 57sts.Work straight until sleeve measures 22cms ending with a wrong side.My query is when do I increase for the plain pattern or dont I have to increase.anyone able to help me I have just started knitting

Yes, for a sleeve you would have to increase. Just follow the instructions for placing the increases.