If you are the new owner of the property the previous rent agreements do not provide and you have to give them eviction notice as you are the new owner of the property and in case you want to continue with these tenants then you have to enter in A new agreement for the Tenancy in case you find anything difficult after the eviction notice then you can file eviction suit in the Civil Court to get them evicted by the court.

the property is purchased by you so you have all the legal rights to execute the eviction

You can sue them for rent. The best course of action would have been RAE (rent and eviction) suit, but since you're are not interested in eviction.... It's up to you. 

However, I must clarify that only rent suit will take​ cosiderable time and you will end up fee whether it's worth it? Hence you are best advice to go for Rent and Eviction suit

. Yes after the expiry of the present rent agreement with those tenant you can make a new tenancy agreement on fresh terms and conditions with fresh rate of rent.

2. If they do not listen you can start eviction procedure so they may get scared and increase the rent.

3. Otherwise on their eviction you can induct new tenant on new rate of rent.

 rent control acts have provisions for a court to fix standard rent and permitted increase in rental each year.

Section 8 of Kerala Rent act provides that if the tenancy extends beyond a period of three years, the rent payable shall be increased by twenty per cent in every three years.

File standard rent application under rent act sec.12 for increase the rent
Where the suit property situated .file civil CMA under rent act for increase the rent which is around near your property and provide evidence and increase rent

Dear client, 

Issue notice for increase of rent, certainly tenant will not bother. Than file application in court for revision of rent. Provision in rent control act.

You can give a notice seeking enchaned rent or eviction on completion of the agreement period this time. You can seek the enanchement of rent as per provision of rent act.

There is no other legal way other that eviction suit for evicting them.

1. You need to consult a local lawyer for this. In the rent control acts of many states there are provisions to file a petition in the court of rent controller with a prayer to determine the standard rent. So if such a provision exists in the statues operating in your state as well then you can adopt that remedy.

2. If no such provision exists in your state then you can only seek eviction on the ground that you require the premises for your bona fide personal use.

Until you dont initiate any legal steps in this regard you cannot achieve your desired object in this regard.

You first issue a legal notice to the tenants intimating the enhanced rent to be paid by them every month in the future  and may also confirm that the unwilling tenant may vacate the premises.

If the responses are very poor or the tenants do not comply with the demand made, you may file an eviction suit ion the same grounds,without any strict legal action, you will be made a fool by the tenants for many more years this way.

1. As per the information mentioned in the present query, makes it clear that you wish to increase the reasonable rent amount and the same is your right also as per law.
2. There has been provisions in every state rent law to get the rent increased by approaching the rent controller of the area who seats in the district court of the concerned area/ district.
3. Once the rent has been fixed by the rent controller then tenant is bound by the same and thereafter, you will not to approach the controller time and again, as after one time increase there will be increase of certain percent after every three years.
4. And if not complied by the tenant then they may have to vacate the property also.