In the following section, I will assume that you are using a web host running a version of Apache to serve the pages. If your server is using a different software suite (LightHTTPd or IIS for example), the names of the variables will remain the same but the place where you set them will be different.
If you indeed had a memory issue, you could try increasing the PHP limits for your webserver. Most people will not be able to edit the Apache or PHP configuration files themselves so you should edit the .htaccess file in your Joomla root folder.
After opening up .htaccess you should add the 'memory_limit' variable, if you have problems uploading photos because the upload buffer is very small, add the other 2 lines as well:
# Allow uploading images or archives up to 128MB in size - modern cameras create images of 10MB or more making a large upload buffer required
php_value upload_max_filesize 128M
# Increase the HTTP POST buffer as well as it should be able to hold the files that are uploaded
php_value post_max_size 130M
# 64MB should allow the manipulation of 15 megapixel photos or more - most hosts use 16 or 32MB default which is not enough
php_value memory_limit 64M