There are many reasons you may need to redesign your website ranging from compatibility with different web browsers and clarity of information to the visual appeal of the site.
Compatibility with different browsers
It is important that your website can be viewed and has a consistent look on various browsers such as Internet Explorer, Firefox, and Opera. If websites are not properly designed there can be serious functional and graphical issues as browsers upgrade their software. These design issues are a good indication that your website needs updating and redesign.
Visual Appeal of your Website
As time progresses, the technology and graphical techniques available to websites improve significantly. The trendy and professional looking website that you had 5 years ago is probably not up to date with current trends and styles making its look and function outdated. In this case you should consider a redesign of your website. There is a good chance that a skilled web designer may be able to work with your current design and modify it however it is often more logical and cost effective to pursue a total revamp of your website.
The Navigation Has Become Confusing
As websites grow, so does the linked content. Your site may have started with only a few pages and links, but has grown to have so many links that it is challenging for visitors to navigate. It is important that as your website develops you keep the design updated to include drop down menus, a smart layout, and collapsible navigation so that all of your content has a proper place, and visitors to your site area able to easily navigate from page to page, and topic to topic.