If it is a colo server If you have all the old file feel free to run the new webalizer on them. Webalizer holds its historic information in text files so you could just move the old files to the new server (back up what is there just incase). Note I havn't told you which files or there location, you would need to read enough of the documentation to figure out how to safely do the transfer how to find the files on both the old and new server woudl be apperent from the docs. If you have a hosted website but no ssh/tenet access: Email the support staff asking for the procedure. The procedure, if available, would be based on their answer not an industry standard.