Entries that haven't been posted for previous years will affect those account balances once you post them.  Before you post them, you should get a printout of the unposted entries so you may further audit which accounts, the effect on each account, and decide what is best to do about them.  For example, if the affect on one asset account is DR = CR, there will be no change to that account.  But if DR <> CR, that asset account will change in the previous year as well as every year after that including the present period.     Use GL - Reports - Entries - Entries by Account and select the New Transaction File to create the printout for further evaluation. 

How can we delete them without posting them? Thank you?

This in one solution found in Knowledgebase:  https://support.na.sage.com/selfservice/viewdocument.do?noCount=true&externalId=44666&sliceId=1&isLoadPublishedVer=&docType=kc&docTypeID=DT_Article&stateId=4089&cmd=displayKC&dialogID=267913&ViewedDocsListHelper=com.kanisa.apps.common.BaseViewedDocsListHelperImpl&openedFromSearchResults=true

Here is another solution but requires the new transaction file only contains the entries you want deleted:  https://support.na.sage.com/selfservice/viewdocument.do?noCount=true&externalId=17875&sliceId=1&isLoadPublishedVer=&docType=kc&docTypeID=DT_Article&stateId=4101&cmd=displayKC&dialogID=268039&ViewedDocsListHelper=com.kanisa.apps.common.BaseViewedDocsListHelperImpl&openedFromSearchResults=true

You need to rename the New.glt file.  See KB article 17875