Tim,
When you mean too big, do you mean the photograph is physically too large in the post? File size should be ok as you have uploaded the pictures to your album. When uploading in to a post, click on the camera icon (insert image from album) and choose the correct photograph for the post, all as previously described by Colin. A large photograph will appear in the post, click on the photograph to highlight it, then click on the previous icon (image) and insert the correct size in the 'width block'. You can also adjust the height, but normally the 'lock ratio' icon keeps the ratio correct. Click in the post to accept and 'post'. From personal experience the best sizes to enter in the width box are 300, 400 or 450.
Hope this helps
If any further difficulties please send a message and I will upload your images to one of my albums and post.
Edited By Tony Hadley on 15/07/2016 09:55:26