GRE

GRE:
The test is required for admission to most graduate schools and a growing number of business schools.
The GRE consists of a 60-minute Analytical Writing section - with two essays at 30 minutes each. There are two 30-minute Verbal Reasoning sections. There are two 35-minute Quantitative Reasoning sections. There's also a 30-35 minute experimental section that can be either math or verbal.
Offered as a computer adaptive by section exam in the United States
GMAT:
The test is required for admission to most business schools.
The GMAT consists of a 30-minute Analytic section with one essay, a 30-minute Integrated Reasoning section, a 75-minute Quantitative section and a 75- minute Verbal section.
The GMAT is a computer-adaptive test.
The overall, or composite, GMAT score ranges from 200 to 800 in 10-point increments.

Hello Nikita Gupta,
You can look at these:
1) Jamboree Education (P) Ltd
No 32, 3rd Floor, Alice Apartment, Above Arasa Shopping Centre S.V Road, Andheri West, Mumbai
Phone:022 6513 3354
2) Imperial School and Study Centre (ISSC)
Santacruz Branch: Office no 32/33, Dheeraj Heritage, Santacruz West, Mumbai 400 054
Phone: 022-26605549 / 9167991339 / 9819698184
3) Collegepond
Vile Parle Branch: 108, Avon Arcade, B wing, Near McDonalds, Opposite Bank of Baroda, Station Road, Vile Parle (W), Mumbai 400056
Phone: 022-26195832 / 9833773135 / 9819888609
4) FACT-Foreign Academic Consultancy & Training
Thane Branch (Head Office): Gurukul Campus, 3, Jyoti Society, Behind McDonalds, Naupada, Thane-400601.
Phone: +91-22-25397777 / +91-22-25393991.
5) KIC Education
Andheri Branch: 102, Agarwal Golden Chambers, Fun Republic Lane, Off Veera Desai Road, Andheri (W), Mumbai - 400053.
Phone: +91-22-67104089 / +91-22-26743117

Top Institutes in Delhi for GRE and IELTS preparation are:
1. British Council
British Council
Address :British High Commission, 17 Kasturba Gandhi Marg, New Delhi, Delhi 110 001
Phone : 1800 102 4353
2. PlutusAcdemy:
Address :C-59 , sector 2 Noida
Phone : 0120-4308958
Focused on IELTS and TOEFL preparation of students also runs online IELTS classes with teachers from UK. Created good name in short time.
3. Fateh Education
Fateh Eduation
Established in : 2001
Address : 6/15, First Floor, East Patel Nagar, New Delhi 110008
Phone : +91-11-6544-7770 / +91-11-3255-0425
4. Megamind Consultants
Megamind Consultants
Address : Megamind Consultants Pvt Ltd. SOUTH DELHI, E-14, 1st Floor, South Extension-1, New Delhi-110 049.
Phone : +91 11 4601 3774
5. Manya Abroad
Manya Abroad
Established in : 2002
Address : B 7/2, Ground Floor, Okhla Industrial Area, Phase- II, New Delhi 110020
Phone : 1800-102-4646
6. TEAMS ( Tropical Education and Migration Services )
Established in : 2008
Address : 309, 3rd floor, Suneja Tower-1, District Center, Janakpuri West, Delhi 110058
Phone : +91 011 45503075, 25550000
7. NAM Institute of Professional Studies
Address : H-68, 2ND FLR, SOUTH EX-1, New Delhi- 110049
Phone : 011-24626548/49, 40598564/65
8. Eduvirt
Address : Benito Juarez Rd, New Delhi, 110021
Phone : 011-24102000
9. Destination America
Established in : 2008
Address : 46, Vinobhapuri, Lajpat Nagar 2, New Delhi 110024
Phone : 011-46540393
10. Verbal Xpert
Address : B 1/1, Near Janakpuri East Metro Station, Opposite Metro Pillar Number 542 Adjacent to Andhra Bank, Janakpuri, New Delhi 110058
Phone : 011- 45720366
11. Veta Global Institute
Veta Global Institute
Established in : 1981
Address : B-3/49-A, 1st floor,Near Bhajanpura Petrol Pump Station, Yamuna Vihar, Delhi, Delhi, 110053
Phone : 9312066612
12. Institute Name : Study Smart
Established in : 2012
Address : D-62, 3rd Floor, Near Dena Bank, South Extension 1,Delhi, 110049
Phone : +91-11-64000090 / 91/92