Backup replacment and incremental issue

Dear friends
i need your help in this . i am now having acronis true image for servers and i schedule a weekly Full backup every Monday and daily incremental backup , it works fine for the first week , after the week finished and it start to backup my data in a full backup again in Monday all before incremental backup corrupted . i think that happen because it replace the full backup because i tell it to do so , so i can save space as it backup like 100 GB for this server only . so is there is way or a plane i could make full backup replacement without corrupt the daily backup before it ? i thought in make it backup incremental for month but this will only delay the problem , hope you advice as this is very important . Thanks