I wonder if I can enter with student visa like tourist for 4 days. The problems is that I changed the date of my school and the visa does not include the new date but i will look for a house and I will back to my country. I will show student documents, return ticket and accommodation. It is a violation?
You have a student visa and you want to come early as a tourist.
This situation is covered in Paragraph 30C of the Immigration Rules, which says...
30C. An Immigration Officer may cancel an entry clearance which is capable of having effect as leave to enter if the holder arrives in the United Kingdom before the day on which the entry clearance becomes effective or if the holder seeks to enter the United Kingdom for a purpose other than the purpose specified in the entry clearance.
Or in other words, trying to enter early invites cancellation of your visa and getting you sent back home to make a fresh application. The start date for student visas is carefully managed by UKVI so as to leave a sufficient buffer for securing lodging before the session starts. Trying to secure lodging outside of that timeframe is an indication that you are entering for a "purpose other than the purpose specified in the entry clearance" (i.e., not a genuine student). The same thinking applies for a person who wants to be a tourist on a student visa.
The key word in the rule is "may". The IO can also determine that your intent is reasonable and let you in. If that happens, your entry clearance will be stamped, and you will enter the UK. The downside to this is problems when your visa nears expiry because you may hit the T4 cap before finishing your course of study (especially if you need to resit an exam). The T4 cap is a hard maximum and there is no latitude for discretion. You should also note that IO's will often call/email the sponsor when an arriving student appears to be abusing their visa, and sponsors have the option to revoke the person's CAS at that time.
What happens will ultimately depend heavily upon your personal impact and articulation skills when the IO asks why you are arriving before your start date or why you are entering as a tourist (if the IO asks you to take a seat in the secured area, it means things are going badly).
Because your question has to do with entering as a tourist, we can answer it on this site. If you have future questions applicable to students, please use the Expat site.
If you changed the date of your school and did not correspondingly get a new CAS, you may find yourself in trouble. But this is a matter for Expats; we can't help you with that on this site...
NOTE: CAS = Certificate of Advanced Studies