We have migrated from Tridion 5.3 to 2011 and want to remove all the templates which are in VB Script. Some of default templates(in VB Script) provided by Tridion are being used in our application. Can I safely replace these default VB script templates of version 5.3 with the default templates provided in 2011 version?
The output of the templates is slightly different from the old ones. I suggest you check how the default templates are actually being used on your websites (they are quite ugly, so I would be surprised if they were actually used on your live sites).
Perhaps the one to be most concerned about is the Default TBB which had functions that could be used by other VBScript templates. So double check that one first.
As @Nuno suggest - do a lot of testing in DEV to ensure the impact of the change is acceptable before doing this in production.