Joomla site alterations and advice

I have an existing website that has a few display issues - nothing too major but need a little assistance with making a couple of changes to the layout. The background image on the home page displays so that it automatically resizes if the window is made smaller - i need this to change. Also the main menu position moves across the screen to the left when the window is resized or if it is viewed on a smaller resolution screen. Is there a fix to this and could you help to make the neccessary changes. Thats really it - nothng major and i have already posted this job however was let down by the previous freelancer so really looking for someone to do this ASAP and be reliable and communicative. Thanks